My stepson is angry at his mom and feels it's his fault she left?

That's very sad. It is hard for him. He may blame himself, but he may just be so hurt and angry, wanting to hate someone who he really loves. My mom dropped me and my two brothers off at school one day when I was in the 4th grade and didn't come back. No call, no letters, not even a Chistmas card. She had called our father who lived out of town and said he better get to the school, she wasn't coming back.He came, and he told us she didn't want us, we were a burden, and now we ruined his life, too. She was gone for years. Then she came back and promised she would come see us on Christmas that year- and then she didn't show up. She kept doing that, making promises and not keeping them. So I know how he feels, it's hard. You feel stupid for believing in someone like that, but it's your mom, how can you not? And you want to be mad, and you want to hate her, but you can't. It's really hard on a kid. Make sure you tell him how wonderful he is, that he is special, how much you love him. The best thing you can do is be consistant. Give him someone he can count on, show him some people do actually keep their promises. Never say anything bad about his mom, no matter how horrid she is, that just hurts a kid too much. Counseling is probably a good idea.