Warning: Long. Please no negative comments

I pretty much had an arranged/forced marriage. We only knew each other for seven months before we married, and we've only been married for seven months (together a little over a year). He's abusive and only cares about himself. I had to leave my family to be with him but he keeps putting off when we can go back to see them. It was August, but then 'someone else got that two weeks off work' so he couldn't (no one else did, I checked the schedule). Then it was February but 'the weather will be too bad to fly'. Now supposedly it's April, but I'm not holding out much hope. He ignores me all the time, only showing interest in me when he wants something. He uses me for money, and if I try saying no he gets angry and violent. He threatened to kill my guinea pig because I said no to buying him a $200 gaming controller. It's stressing me out so much. I can't afford a divorce and he refuses to file despite the fact he keeps announcing he doesn't love me.
That being said, I'm not helping the situation. I can't leave but I don't feel married. I feel like it's just a contract. So I've been having an affair with his half brother. He's completely different, he looks after me and I know that when he says he loves me, he means it. He shows it all the time we're together. He knows what my husband is like but there's nothing even he can do. We've talked about a life together and we both want the exact same things. My husband and I have NOTHING in common. I feel like I have to wait until something happens and I can finally get away but until then I feel so trapped.