I'm confused, what happened?

I have been married for 9 years and with him for 12. About 3 months ago, he left me. We still haven't talked about why he left. He picks up the children every other weekend but he won't talk to me at all. He has his mom call and make the plans for the children. I asked my mother in law if she knows what is going on but she claims she doesn't. Before he left, we weren't having any big problems. I don't know what happened or what I did?