He almost hates himself for doing this.
Theon just wanted to go to the Iron Islands to get his father's help with Robb Strk's fight. He wanted ships to help his friend, and it backfired.
His father didn't like him. He almost slept with his own damn sister because she didn't tell him who she was. His father wouldn't help, and overall he was treated like shit.
But he still wanted to prove himself worthy of his fathers attention. He just wanted to be loved by his own father. And the only way to do that was to take over Winterfell.
But he's hit two bumps in the road. You. And his feelings.
He can't betray Robb, he's like a brother to him. And god's, he can't hurt you like this. You're his best friend. You insisted on coming with him.
He hates himself for falling for you. He's a man, you're a man. He's supposed to be strong and manly... But here he was. Hesitating. He should just take Winterfll already, not sulk about it.