I have two sons 6 and 16 and a stepson who's 10 (as well as a 5 year old stepdaughters(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 He seems sad and withdrawn after his mothers divorce.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. He will occasionally talk to my son, but not often.
Strangely my son treats my ss better than he does his own little brother.
I'm not pressuring anyone to do anything.
My wife and I checked to make sure my son wasn't bothering his step bro or doing anything negative in secret. He wasn't.
You see.as a kid I was an only child with no cousins and relatives my age and only my mother for support, so as a teen I had to build a second family out of friends, so I don't get sibling stuff.
His father is out of the picture and his bio mom is a good woman.
My son has a lot of friends so I'm surprised that he's putting so much effort into this.
I saw one good sign though, my SS started calling my son by his actual name instead of "you"or something derogatory!
I don't think I've ever heard my SS laugh.
Is it even possible for stepbrothers to get along or be close?
Is there any hope that things could turn out all right for my SS?
Is there anything me or my wife should do?
I would deeply appreciate any advice and/or comments.
Remember, I know nothing about sibling relations all of my " brothers and sisters" are friends.
What do I do? In your opinion.
Am I being too lenient with my SS?