Sam rented out warehouse space with some friends of ours once college was over. I used to visit while he was working and walk in on spot-lit, hulking pieces of rusting metal cut sharp and angled precariously, white hot sparks showering down and him behind a welder's mask, blow torch in hand, usually halfway up a rickety scaffold tower too involved to notice me. Just like he is in so many of my pictures – he was too full of inspiration to stop.

They always had the radio on and I always used to wonder what the point of that was. Above the grinding, sawing, shrieking of the machines, there was no chance any of them could hear it.

Between us, we'd painted a mural on the back wall – a collaboration between the three of them, me and another couple of friends. It was a lot of colour, mostly. Three sculptors, two photographers and a textile artist: we had little talent with a brush between us. It was never meant to be a work of art, just our mark on the place.

There are glimpses of the bright blues and oranges in the background of a lot of the shots I took of him working in there. That workshop was always a good place for inspiration. The stage sets the kids at Ewan's school had been working on reminded me a lot of that time – of a puddle of red soaking into the concrete floor, of paint flecks that turned to smudges, turned to swipes with brushes and rollers down chests and soaked t-shirts and shower water that rainbowed down the drain. Pastel shade soap-suds on his chest and the handprints we left on the wet, white tile wall after he tried to hold me up and fuck me with my legs wrapped round his waist and it turned to slipping, gasping, laughing best sex in the world that now is only a vague recollection.

Sam worked two-tone. Either in elbow length gloves and overalls, muscular and sweating – the brawny side everyone expected - or quiet and concentrated, in reading glasses with his drawing board and his ruler in the spare room of the place we rented, working out angles, dimensions, stress points, with technical drawings and models made of corrugated card. That was the side only I ever got to see.

"What d'you think? Imagine it twenty times bigger with the arch done so it wouldn't fall and kill you."

He got contracts with councils and the highways agency for sculptures in the middle of roundabouts, at the side of motorways running the length and breadth of the country, in city centre squares and parks.

Some of them he'd scrawled with secret lines while working, that he'd tell me in husky, whispered words, with his smile against my ear while we stood opposite this church or in thatMiddle England town for the unveiling.

"Bend over Nate and spread your legs, I've an ache I want to ram home. Tangle-cocked I want you and breathless my sweet, with sweaty groans. Last night, bugger-all, teasing fuck-whore you had me wakeful and restless and you true-sucked and gone to sleep."

His James Joyce phase, he told me.

Richard Fuller – the owner of that chic gallery – had always tried to get him to scale down to something his small gallery could tap into, because you couldn't get much of his work inside. The man had tried the snob line on him – that no artist had really made it until he had his own show and there were reviews. Sam had snorted at him and just resisted waving his cheques in his face.

"Do you know how many cars travel on this road every day? Every single one of them sees my sculpture. What do I need an exhibition for?"

But he did one – we did one. My photographs shrank his sculptures down so that Richard could frame them neatly, set them on the walls and make sales. Two artists for the price of one. "Nathan Owen on Sam Richmond" ( "but only sometimes," Sam had teased, with his dry smile and his teeth to my neck. "When he's really in the mood.").

Following my conversation with Neil, I'd been back in touch with the gallery to accept Richard's proposal. It was difficult, but it made sense – mostly financial sense. Whatever I'd rather run away from and keep as private as possible, there wasn't another choice and painful as it was, it needed to be done. Part of me thinks I shouldn't have needed the promise of some reward at the end of it to finally take that solid step towards moving on, but the rest of me knows I'd never have made it alone.

The exhibition was going to be called "Sam Richmond: Public Art, Private Places" and it would be very different from that first exhibition. Sam had done a few smaller pieces by the time he died and Richard had acquired a couple, but he wanted the show to be more than just Sam's work. He wanted Sam's life and secrets as well – the decoded mystery of those words that had started to come visible on the surface of some of the sculptures as the patina had weathered over time – and as he'd already said, he wanted pictures of Sam as well. Even Neil began to look concerned once he realised that that glimpse of 'private' wouldn't be limited to photographs.

"Context, 'Than. You know how it goes. We can't structure anything without context, and you're the only one who knows what they're all about."

But they're not about Sam, Neil had signed, face outraged, the day I showed him the scraps of paper clipped to images of the sculptures holding those secret, scrawled lines writ large. You can't let him put them up.

Our sex life, our love life – my past with another man in vibrant scraps that must have seemed a patchwork of days on end in bed, super-charged libidos and never enough of each other's body; I understood entirely why Neil's face was suddenly unreadable and his smile had vanished. We weren't raw energy like that. Between us was more of a slow burn and these lines must have made him wonder why I wasn't that way with him.

"Neil, it wasn't..." Wasn't always like that, I wanted to tell him. I should have told him it was mismatched schedules and travelling apart as often as together – should have told him it was half the year in cars, travelling up and down those motorways, and that was why Sam had taken those commissions at first – just so I'd see something of his and the chances I'd remember to call him in the evening would increase. I should have told him we had blistering rows sometimes and had to keep to separate rooms to avoid the punch up. But when he'd written those words, it was like that. And how could I say that those words – so full of love and need, so full of everything I'd missed and hated him and myself for ripping away – were anything less than true?

"Help me choose pictures, ok? I'll talk to him about the rest."

Negatives of Sam weren't something I often looked at with a critical eye, but finding the good images when that's what you've trained yourself to always do was no great task, once I detached from the subject matter as much as I needed to. Surprisingly, Neil was the one slipping things from the pile I had okayed onto the stack of 'maybe's.

Too sexy, he explained, head tilted in a stern shake as he vetoed another choice – the pair of us in bed, naked as far as the picture frame stretched.

"It's a gay gallery," I'd retorted, my patience thin and stretched taut. The only way I was doing this at all was by detaching entirely and I couldn't factor out everything I wanted to, so I might as well let it all through and pretend not to care that a good deal of our relationship was going to end up on public display – that all of them would look at me and know I was the guy driving the car and think how tragic for Sam, to be killed by the one he loved.

It's about him, not you together.

"So?" Sam was too shrouded in my memories for me to separate him out and it took a while for me to realise what Neil meant.

His eyes narrowed and he shook his head, sighing deeply.

Too sexy, he repeated. Then his eyes widened, tugging at mine as though he was hoping I'd understand.

Jealousy was what I came up with in a rather guilty glow and somehow my lips eked up at the corner in an almost smile.

"You're not even my boyfriend," I reminded him, still annoyed about this challenge of his. It had been his idea for me to go through with the exhibition.

His jaw clenched and his eyes turned dangerous and deep; the smile and the assumption were mistakes. I almost thought he wouldn't bother with words, but he did and that was worse than any silence could have been.

No. I'm not. Frustrated with the speed of communication between us – at how slow he had to go for me to follow, he snatched up the preliminary flier Richard had sent me, advertising the proposed date for the show.

Nathan, the show like this? Not about Sam. One finger jab to my name, one finger jab to Sam's and a gesture to the images littering the floor ready for selection helped him make his point. So in love. His face screwed up as he mouthed it as though the thought hurt, but he still managed to act an expression of enthusiasm and I knew he was aping the responses he expected from the people who would see it. Tragic. Really sad.

The reporters? he mouthed, miming flicking out a notebook – the palm of his hand the paper, fingers gripping an imaginary pen. "Oh, and who is this?" His voice was a shock and that was the first time I'd heard it apart from his laugh. His words were far more garbled than Ewan's ever are – thick, mangled and misshaped – just sounds really, but with concentration I could pick them out – the animation of his face, the slow rise of his eyebrows and his overacted eyes as always helped. "New boyfriend? No. Still loves Sam. Pity fuck, must be. Deaf. Too stupid to speak."

"Neil!" Again, I had that urge to step closer and touch him to force him to listen, but he stepped back, one hand up to keep me back – telling me he hadn't finished yet. From the look in his eyes he'd been expecting the shock I know I showed at the sound of his voice, but all I felt was guilt about it. I barely knew what to say – whether to be insulted, or scared that he'd hit on some truth even I hadn't realised yet. It didn't feel like the truth but my voice failed in a garbled pile of words I couldn't use, terrified that he did see it that way.

He shook his head firmly, eyes solid and he blew out a breath that was every inch frustration. I swallowed fiercely, expecting the worst – him changing his mind, walking away, leaving. Relief surged through me when he raised his hands again and his face cleared, both shaping calmer, slower words with the tug of annoyance in his eyes fading. I know - not what you think, just what they might. So don't set it up like that Nathan. Please.

Near on quaking, I nodded hard. Losing Sam had already happened and there was no way to change it – I'd already wished myself blue; memories couldn't force away my future too.

"I'll keep it about Sam," I promised, shifting the bed picture into the 'no' pile.