You really think this guy has his life together? You actually answered your question in your question... Why on Earth did a guy like that pick... Well, that's because he's a guy "like that". He's actually not a professional who has his shit together. He's on TS's level which is why they've ended up together.

I hardly know these people so I could be wrong on many counts but he strikes me as a simp in disguise. The kind of man who bases his value from the attention women give him instead of having his own value for himself come from within. That's why he'd put up with a girl like TS because she offers a lot of positive reinforcement for his self-esteem because of her looks and fame. That type of guy is precisely the kind of guy that would cheat though; however, TS is likely going to have a better chance to tame this sort of guy compared to any other girl. TS knows what kind of guy he is, likely because he's exactly the kind of guy she has historically dated. TS isn't a quality person either. Sooo they're probably good for each other.