I appreciate the advice, thanks. I'm perfectly happy for BF#2 to be mono if he would like to, but he also wants me to be the same, which is the crux of the matter (apologies if I didn't make that clear in my first post!) I can respect that feelings can change/evolve over time, but unfortunately this has only been from one side.
I can sense an ultimatum coming, and I know he doesn't wants to do so, as he thinks that I'll choose my lifestyle over him (I'm not sure at this point what I'd do if that happened). Maybe I'm just delaying the inevitable by trying to ride it out.
As for counselling, as good an idea as it is, #2 doesn't like the sound of it, and neither of us can afford it at the moment. I feel like Sisyphus pushing that ball up a hill - every time #2 and I make some headway in our feelings, it comes rolling back down again.