A couple of random thoughts:
- As hard as it is to believe and through no good intentions on her part, your sister did you a favor. This guy was real trouble and if it wasn't your sister, he would have gone off with someone else.
- You are going to have to make a decision about what you want your family life to look like for the next 30-40 years. If you don't want an ongoing feud, you and sis are going to have to come to terms. Maybe you just need a frank sitdown where you clear the air and maybe you will never really be tight again, but I don't think you want to hold this grudge for the rest of your life.