Your mom may just have a lot of suspicions only, but her gut instincts could very well be right. And she may even have proof. Either way, I'd advise you not to ask or concern yourself with the details. They won't be pretty. True or not.

They evidently have problems. Every married couple does. If you start learning details you may start siding with one of them. That's what I think will cause you more more grief. Just accept that they might not be able to work them out. A lot of couples do resolve things. My wife and I did.

You want them both in your life for as long as they're around. You can best help them by staying neutral. They both love you and neither wants to see you hurt. They know this is going to affect you and your sister, a lot. Just let them know how much you love them and no matter what, you always will.

Your sister is going to need your help, too. Talk about it with her. Be honest with each other. Together, you'll each get stronger.

Above all, do not try to put any of the blame on yourself. Neither you or your sister had a single thing to do with it. Using kids as an excuse is just complete BS and an unwillingness to accept responsibility.

Problems with kids is normal, too. And couples in a strong marriage face those problems together. They don't use them as an excuse for a bad marriage.

I'm sorry about your situation. Good luck to you and your sister. God bless both of you.