I'm gonna have to be **R E D P I L L** for a moment and wager the main reason this guy is getting YTA'd is he sounds desperate for sex. Being desperate is a big turn off for women and they hate desperate men (since they have to deal with them and the fallout). Fact that he was banking on it being a concert the girl was interested in him implies he is not very attractive to begin with.         Lets imagine if the situation was reversed. Let's say he first asked his co-worker out on a date to the concert and got a yes, but then found out his other friend was a really big fan and decided to invite her instead. The foids would fawn over this guy for not only the surface level "niceness", but demonstrates  he is not desperate for sex, implying he gets it so easily he is willing to sacrifice an obvious shacking situation for a friend. The irony being its massive douche move, since it knocks down the girl who likes him, and will make her forever wonder if they didn't do more in that hotel room than sleep in separate beds. Shit like that drives people insane.