I didn't doubt that when an eighteen-year-old gay boy said he had a hookup that he meant sex. That's what S. meant when he told me he'd had hookups, and I met S. when he was nineteen. He spoke some about when he was younger than that, too. With S., we talked about how the important thing was that he was safe, but agreed that it was perfectly normal that he'd have hookups. I note that S. is a real person and wasn't dating anyone at those times.
I have no problem believing that Blaine is lonely, damaged, self-destructive and depressed. I wouldn't be surprised if he had more hookups. His younger fans will be in despair, and it's not really an appealing image for them that Blaine would have casual sex, but there's a certain truth to it. It's more disturbing to me that he'd probably do it because he's in a bad mental state. Blaine doesn't think that he matters.
It doesn't seem like that many fans had issues with Puck having sex with women twice his age, although I think that certainly contributed to Puck's damage. Some of the student characters were presented early on as having had a lot of sex. Sam lost his virginity when he was working as a stripper, in a "might as well" way, which I found depressing. Jake is being presented as being a "womanizer." Blaine had a nicer image for quite a while. That's changed.