Me personally I'd try to get over the guy. If he disses you and goes on about you then he's not worth much. And if this girl is really your bff you should be able to talk to her and let her know how you feel about all of it.
Here's a saying I follow closely.."Don't push your relationships if they were meant to be they'll be." hope I helped atleast a little. Good luck!(=
Talk to your bff about it! If she really is your bff, she'd understand your feelings, no matter what guy she was dating. I wouldn't suggest telling him, it doesn't sound like he feels the same way toward you! As for them still dating, who cares? If it's your bff, you should feel happy for her!