Ask HN: I'm falling in love with my already involved cofounder,what should I do?

I'm in a really crazy situation, I co-founded and I'm working at a startup with one of my best friends and his girlfriend.

During the last few months I'm completely falling in love with her and she's too (my friend obviously doesn't know)

I deeply care about everything: the startup, my friend and her, and this is like a bomb which will cause many break ups once it'll explode.

Has anyone of you been in this situation? How did it go and what do you suggest to do?