LMo, You did not mess up. Everyone is entitled to an opinion. I think the person your step-mom is mad at is her son. As a mother of 3 boys I can't imagine that they would ever do anything wrong!!!HAHA! I do know that they are not perfect and will eventually make mistakes. I think that your step-mom just doesn't want to imagine that it could have possibly been any fault of her son. It takes two to make a marriage work and it also takes two to make it fall apart. I think you should encourage both of them to go to marriage counseling! They may find out how wonderful it is to fall in love with someone for the second time.

I would call your step-mom and tell her you didn't mean to offend her and your comments did not mean that you don't love your step-brother or her but only that you would are open minded enough to see the whole picture. It doesn't matter who's fault it is or why she is leaving it only matters that they try to work things out through counseling or separation and counseling so that their son has a chance at having his world stay intact.
Hope it helps

jac