I don't think we can ever get into anyone else's marriage. My stepsister had your sister's marriage for 40 years (4 children)! Lots of us told her to leave him and she would not. He finally died and she remarried another college boyfriend, this one wonderful (both in their mid-60's). It's your sister's life and she's going to live it how she lives it no matter what anyone else's input. I wouldn't take what happens to her personally. Her husband might grow up/mature and get his act together or might not but it's not your problem.