First thing: everyone has different views on love.
Second: I have no idea what poems Burn's written but from your essay I get the gist of it.
Third: to be honest no one has the right to judge you because everyone is entitled to their own opinion.
Now back to my opinion: I think what you have written justifies what you feel, and yes there may be those who won't like it because they admire a person for their talent, but I do agree that it is not nice to write something when you don't feel it. Words without feelings or emotions are meaningless, and to break a person's trust whether it is a man or a woman is heartless.
I don't think people should write or give something to a person they are with if they don't truly appreciate and respect them, even if it is not love, because that's just a way of keeping them with you. I think Burn's felt insecure, but yes he shouldn't do something wrong e.g. have an affair and then not take responsibility for the outcome. (if he hasn't done that is)
But I do hold love in high regards and like you said, you're relationship with your husband is open and honest, I'm happy for you both because I do know that people aren't lucky enough to find their soulmate like you. I understand that what you feel for your husband is love and him being your first and only love is amazing, but like I said, people have different opinions on love, it' not only for one person, love comes in different forms e.g. for your family, your significant other, your career, your country etc, maybe what Burn's felt may as well be love but on another level for him, but yes he did treat his wife wrong and for that I do not agree with him. You also mention some quotes and he has repeated a few lines about his love, I think that he's trying to convince himself, but the part about him writing 'his only love' that was wrong of him.
In my opinion, if you aren't open with each other, have no trust or respect for each other then it isn't love and I feel Robert Burn did not respect his wife let alone women in general so yes, I do agree to some extent that what he felt wasn't actually love and yes, you can't write about love for one person if you don't know what it feels like, I don't that's why I never try, because I always think that love is different for others, if I do write about love, it's in the form of appreciation for my family or nature but never about my significant other, because I've never met him and don't know whether he exists, lol.
Okay, getting way too serious, but you haven't written anything so wrong, you've just talked about your feelings and like I said, everyone's entitled to their own opinion.
Maybe, it's not right for us to judge Burn's character or poems, but one can't really help themself if whatever they see or read and think that it is wrong. After all we are humans and it's in our nature to perceive things differently, whether people agree or disagree with you.
Tecna ;)

No it's not a poem, but it is not fiction, either. It had more to do with poetry than anything else, so here it went. Enjoy.