I have two sons 6 and 16 and a stepson who's 10 (as well as a 5 year old stepdaughter. (she gets along well with everyone). However my ten year old stepson never warmed up to me, he seemd kind of scared,of me, so I try to be sensitive to his needs and kind, I don't try to discipline him. He seems sad and withdrawn after his mothers divorce. My eldest son has tried really hard to befriend him. He have him his room, tries to get him to laugh or play video games , sports etc. but my step son yells at him that he's not his real brother. The only time he was semi-thankful was when my son protected him from a bully. My son stopped trying and gave him space, but for some reason after 6 months he started trying really hard to befriend his stepbrother again and is still trying.

It's been almost two years and me stepson is only close to his biological mom and sister.
Can I do anything to make him happier and more comfortable. His school therapist says he is not depressed and he gets good grades, but he seems pretty sad to me, always holed up in his room.
Any advice would be appreciated. Why do you think my son trying so hard to bond with his younger sb?
I have never pressured my son to bond with his stepbrother , I told him to let it be, but my son will wait a month, then try again, with no luck, why does he do this.
My son tried to hug his sb on Thanksgiving and got a punch in return, I can't get that angry at my SS, I did tell my son to leave him be.
Don't get me wrong my SS is a good kid and I do care about him and I can't help but to feel really bad for him.
He won't even talk to me directly.
Strangely my son treats my ss better than he does his own little brother.
What's going on?
Tom