Since it hasn't been said, I'm betting it's something like this...you have a 'connection' with him through bikes, that she'll never have and probably more attractive than her, so she's jealous. Why he's not standing up for himself and fighting it, well, that's only a question he can answer. Sucks when it happens, but sometimes you lose friends to bad relationships. He'll come back around one of these days and realize riding is much easier to deal with than relationships.
