My boyfriend's best friend wants me?

He texts me all the time and I was just thinking it was because we're all friends, then our conversations kept getting more serious. I didn't spill my heart but he kind of did. Then my boyfriend calls me and tells me that Jesse (best friend) wants him to have with his wife?!?! wtf? Dustin (boyfriend) says heck no, then Jesse asks his wife if they could have casual with other people and still stay together. Cie (best friends wife) told me he talks about me all the time and that he does everything I do. That she gets jealous of me somtimes. What should I do about this situation if she continues to be with him, because she's become my best friend....?