How to Deal with a Strong Headed Boy

Sounds a lot like my son in many ways.
He's also 12 and gifted.
He's very smart, but can get into a mood every so often.
I'll sympathize, I'll talk to him, I'll give him a hug - then I tell him he can feel sorry for himself for 10 min in his room and by then he'd better be over it.
So far it's never failed.
At 12 yrs old - he can start meal/food preparation.
If he's going to be picky, he'd better start learning to prepare his own meals.
My son's been making his own lunches for day camp all summer.

It all boils down to basic socialization and emotional maturity, and manners and principles.
Teach him these things now, before he gets older.

Also Google Search "Tween Boy Development" and "Teen Boy Development," since this is your son's developmental age, now.
Kids change a lot, at these cusp ages.
Many developmental stages, still.

But he is old enough, to learn basic human coping-skills for any emotion he has.
Even many adults, don't know this.
It is a taught, 'skill.'
Kids are not born with it.

At home, is often where kids let it all hang out.
Luckily, your son does know how to be nice, at school.
At home, is where he needs to learn, boundaries.

He also has his own interests and personality.
But learning 'cooperation' is a very important ability for him to attain. Still.
AND he has to learn that BULLYING IS SISTER... is NOT allowed.
Siblings, should have each other's back.
Teach him this.

Your HUSBAND also has to be a part of this. I don't know why he is saying that you & your son have to work it out on your own.
That is your Husband's son too. A boy, NEEDS direction and nurturing from their Dad, too.

Build a 'relationship' with your son.
See who he is.
He is a kid.
No matter what, a child needs his Mommy.
Don't be afraid of him.

This is a good link:
http://nymag.com/news/features/27840/

How to Talk So Kids Will Listen, and Listen So Kids Will Talk, by Faber and Mazlish, is an outstanding parenting resource. They offer wonderful and mutually respectful techniques to communicate with and draw out kids. It helps you understand what a child already understands, and how to help bring them onto the problem-solving team. I've used these techniques with my 5.5 yo grandson, and already get a sense of how powerful this approach can be. Try it – I'll bet it can help bring out the best in your son, and gently coach you toward more effective communication.

A couple of books you might want to check out include "Disciplining Your Strong-Willed Child" by Robert MacKenzie and "How To Talk So Your Kids Will Listen and How To Listen So Your Kids Will Talk" by Fabler and Mazlish. Some things might be more of a challenge because of him being gifted but deep down he is still a kid that needs to listen and respect you and your rules. I would start thinking about what is really important to you and what you think you can bend on, then sit down with him and calmly discuss your expectations of his behavior - i.e. absolutely no bullying his sister; if he doesn't like what is being served for dinner, he can have a PBJ sandwich but he must make it himself, etc. Let him start trying to come up with his own solutions to some of these problems and see if by having a discussion you guys can end up on the same page. Don't let him blowing up cause you to blow up too - my daughter is only 4 but also very smart and very strong-willed, and sometimes the more upset I get about something, the more strongly she reacts and we kinda feed off of each other. So I need to remember to keep my reactions in check and try to stay calm (but still firm) and not react when she blows up about something.

Well I suppose instead of out and out facing him about something. Like say a trip to Disney. Say what do you think about Disney World? We are thinking of doing something what would you like to do. If he bullies his sister then they aren't getting along that great lol. But kids do fight. He is right at that age to where he wil be a teen and loose his head. All you can do is be a good listener for him so he wil feel good about telling you stuff.