I don't get it

this guy I met online i was planning to meet. but he ended up getting a girl friend so I stopped talking to him cuz I don't mess with guys that are taken, well just a few minutes ago he ask me if I wanted to hook up. like what is wrong with you? he post a picture of him and his gf on snap and she's gorgeous why would you want to cheat on her guys are so stupid sometimes and no I didn't tell her because I have no way of getting in contact with her