I am dealing with the same issue. Only I am in "love" with my bestfriend's husband. I am a married poly woman. my husband is mono but willing to work at the poly side of himself. This couple means a lot to both of us. She is my BF and her husband in my guy's BF. I am sure that her husband has some feelings for me and my guy would love to explore more with the wife. I have picked up on little signals from her husband over the past few months. Things like lingering touches and "accidental" footsie. I say accidental because that's how it started... then he just let his foot stay in place one day. I did not notice it at first and I don't think he did. It was more of a comfort thing for us... i'm guessing. When we both realized that it was happening we didn't freak out. We actually got better at the game we were all playing (pictionary) and won. He has yet to mention it and he has not changed at all around me and the gang. He has started being himself though. As in, relaxing more. Like my guy and I are not company anymore but family. I love it. His wife is also acting this way. A while ago I flat out said "take my husband, please, you can have him anytime you want..." She just giggled. I know she thinks about it but recent life events have pushed her focus elsewhere. Family and whatnot. I would not even bring this up now. It is not the time. But I am thinking... and waiting.
They know how our relastionship is set up. Only the wife has talked about it with me and she thinks it's "different". She still likes us and trusts us around her family. That's why she is my best friend.
I want to express my feelings, openly, to them but I don't know how to go about it. My husband knows how I feel. Out of all this I am the only one that has "lived the lifestyle" so to say. I'm used to lots of crazy love bunches. I am just sitting on these feelings until I can talk to them about it. The wife knows that I have a crush on her husband. She thinks it's cute. But she also knows that I would not try anything. I think that is why she is comfortable with it. How do I let her know that I really would love to be more than friends... with both of them. I'm not a lesbian but I have fallen for women before and she is certainly 'fallable' in my book.
For the OP, I know how it feels. Not knowing when and what to do or say. Just keep it honest and remember that more than anything they are your friends. That is what I keep telling myself until I figure out what to do next.
Please keep us updated good Sir.