What is it that has you so upset? His comments about your sister? Just because he loves you doesn't mean he's going to love your whole family. I would hope that he is pleasant, kind and civil to them, but he really doesn't have to like them.

Neither you nor your partner can do anything to help your sister get her marriage straightened out, it's something she and her husband have to do. By all means give her a shoulder to lean on, but otherwise stay out of it. You are getting her side, your partner is getting his side, and the truth is probably somewhere in the middle. Right now it sounds like you are bringing her problems into your own relationship and that doesn't help anything.