I'm rely worried about my brother, what should I do?

My younger brother's gay he told me when he was 12 and I was 14 that was 2 years ago I have no problem with it. last week week my dad found out he walked in on him and his boy friend kissing. He has hardly talked to him since and when ever I have seen him talk to him it's been an insult. The over day he spilt a drink and my dad called he a stupid little fa g. Before he found out he was like golden child and now he wont even look at him straight. I thought it would change but he's being down right cruel to him when What should I do should I say some thing to him. I would talk to my mum but she walked out on us 5 years ago. What do I do?