I'm so sorry you are in this position.
I'd never considered myself bi, and I was in a relationship with my bofriend, but I too got very close with a friend. Well, it went "all the way" and we even ended up in a relationship - both of us had never considered ourselves bi.

I know the pain of having that person ripped away from you. To hear you can only love them as a friend. Those emotions are hard to just put away.
I still haven't totally dealt with my emotions, and it's something that's slowly surfacing in T. I think that's the only way I'm going to deal with it.