Is my boyfriend gay?

Me and my boyfriend went out Saturday night with his friend and friends little brother. I'm 27, my boyfriend is 29, his friend is 27 and his younger brother is 18. We went to an 18+ club and we were having fun. We didn't notice that my boyfriend's friend was sneaking his brother drinks and my boyfriend ended up going off on him a little for that because we could get in trouble for that. The brother was wasted, so my boyfriend sat in the back with him and I went to sit next to them. Then the brother started telling my boyfriend how he's always so nice to him and then just KISSED him. Right in front of me! My boyfriend just stood there until the little brother stopped and then said "I think we need to take him home." So we all left. The whole thing left a weird taste in my mouth. I have no issues with gay people. My step brother is gay and I love him. But my dad and my biological brothers would have cut a guys throat if they kissed them. I asked my boyfriend why he just stood there and he said it caught him by surprise. I asked why he was still being nice to him after because like I said, my dad and brothers would have harmed a guy for doing that. My boyfriend said he's not a violent person and knows he was drunk when he shouldn't have even been given alcohol. I just feel weird. Most straight guys I know would punch a gay guy for so much as a compliment. I'm not saying that's right and I'm not saying I wanted him to harm a teenager but I don't understand why he wasn't at least a little angry.