You did nothing wrong, but if I were you, I'd try to patch together some kind of reconciliation or truce between your H and his family. As I think you said in a post to someone else: "blood is thicker than water"--which is pretty unfortunate, but there it is. It's a miserable situation, but you don't want your H estranged from his sister. Could you talk to your husband about how he feels about it? It seems that he's caught in the middle right now, but maybe he has some ideas. I guess that your H's sister is sticking up for her husband? If I were in your place, my first thought would be that my H ought to stand up for ME against his family--and especially if he'd just betrayed me with an affair.
But, on second thought, I think you ought to let it go, a little bit. Just let it slide over your back. BIL hit on you. It happens. Give your husband the space he needs to mend fences. Leave him free to do it. You don't need this kind of conflict. Your husband needs his mother and sister. You want YOUR truth to be known--but I think you should distance yourself from the bad sitch and let H deal with it as he chooses. These family things are just flashes in the pan--tons of drama and then gone in a year.
