How sad for your family. It is hard to watch people you love make poor decisions. I would suggest being as patient and loving as possible. Remember that if you are here for your sister now, if everything with this guy turns out as badly as it looks, she will be more likely to come to you when she has a big crisis in the future.

I know your situation with your sister is different (my family loves my husband), but here are some other thoughts I have:

I got married last year - I also started law school. For a while, I was not able to spend as much time with my sisters because of the wedding, etc. Then I moved to another state! It's pretty hard because we miss each other a lot.

However, now that things have settled down and life is more "normal," we talk on the phone a couple times a week, send each other cards, etc. Things will become better for you and your sister in the long run.