My older brother is in a relationship with this girl whom he's been dating for like 16 months. Now, to be forward, he's pretty beta in the normal sense of the word. They fight constantly and he's a slave to her pussy. He devotes all of his time to her, and she barely reciprocates (among other things). Recently, he came home from a 6 month hiatus to FL to get his life together, but that's another story. He's caught his gf lying and talking to other guys before, yet disregarded those red flags as this is his first okay looking gf (she's maybe 7/10). I'm 100% certain she cheated on him during this time, but i have no proof. Additionally, his first night home his gf claimed how excited she was that he was back and told him she'd like to get together, then proceeded to go out with her friends at 1am on their 16 month anniversary and blow him off. My brother was mad, yet still doesn't realize MAJOR fucking warnings right in front of him. I asked him if he thought she was cheating and he avoided the question. I think he just doesn't want to be alone more than anything. So in a nutshell, I need to help him out. He means well, he's just dumb and refuses to accept red flags. What can I do?