How do you explain an emotion without a name?

I've tried, but heart's impossible to tame

I suppose you could call it a bittersweet sorrow

And I'll wake up feeling the same tomorrow

I tried so hard, and I got so far

But here I stand, no knowing where we are

I'm confused and I'm hurt, but I'm trying to win

But my mind fills with thoughts of the same old sin

How do you look at someone knowing they're going away?

How can you explain how you feel when there are no words to say?