Am I a horrible step-mom...?

I have been in my 4 1/2 year old step-son's life since he was 1. I love him to death, but since having my son 9 weeks ago, it just feels different. To know that I created this little boy, and that he is part of me, is just amazing. I try to feel the same way about my step-son, but to be honest, I just can't. It's even harder because he is a huge handful. His mom and her boyfriend who have 60% custody have turned him into kind of a punk. They shaved his hair into a mohawk, and he says stuff like "sup brotha". I just don't agree with that stuff. Plus, I have said for 2 years now that he needed special attention as far as learning goes with no avail. Now his daycare/preschool provider told me that she hasn't had this much of a problem in all of her 25 years experience. I feel so horrible and guilty for saying this, but it's just not the same - he's just not mine. Have any of you experienced feelings like this, or am I just a horrible step-mom? :(