My son changed his last name to his step-father's without telling me and I'm really upset.
Why didn't he tell you? Is this the first time he's done something like this?
No it isn't, he also changed all of his contact information to his father's without telling me as well.
I'm really sorry to hear that but there really isn't much you can do. It makes sense to be upset that your child favors his step-father. I hope you're able to become closer with your son however.
Yeah I never liked the guy and I'm going to disown him now.
I wouldn't do something so extreme. It is a big deal to disown your son, and you shouldn't do that unless you have a really good reason to do so.