The answer, of course, is that the college student who hangs around high school doesn't have any college friends. High school is the life equivalent of the La Brea Tar Pits: If you aren't careful, you'll get sucked in forever and become a dark, eternally adolescent version of yourself. The fact that he's taking a high school student to her prom may be a "wow" for the yearbook committee, but it certainly isn't doing this guy any favors with his peers. That, of course, means that he'll be hanging around the high school even more, creating the downward spiral that pulls him further and further into the tar.
Your Fun Uncle / Aunt / Your Parent's Fun College Roommate
If you were lucky enough to have one as a kid, there was probably a time when you idolized your parents' fun friend. They were so worldly that they would bring you exotic gifts, like those "cursed" masks from Africa or those knives from Phoenix. They always seemed to have a cool new girlfriend or boyfriend, and they were fun! Every trip to the grocery story had the potential to spontaneously transform into a trip to the water park or an ice cream parlor. They're the person most likely to have let you shoot a gun when you were too young for that to be tinged with feelings of guilt!
Yeah, but she kvetches at an eighth-grade level.
It's only in the cold light of adulthood that you realize all of their seemingly fun behaviors were in fact a flat-out sprint away from the many problems facing them. They weren't happy ALL the time; they were happy to be at your place, because it was the one place people listened to their opinion without them having to buy a round. They weren't spontaneous; they were incapable of completing the errand of getting milk without having a panic attack about where their life was drifting next. They weren't letting you shoot guns at that age because they knew it would be fun for everyone involved, they ... OK, maybe they did in fact do that just because they knew it would be fun.
The point is that the people we looked up to when we were children had some serious problems. That's because children are idiots with idiot priorities. They have no taste and no understanding of the way the world functions. So if you've been holding on to a piece of advice from that drama teacher who took so much time listening to students' relationship problems that their own marriage fell apart, maybe it's time to reexamine the validity of that counsel.
You and your childhood heroes spent an important and wonderful time together. But like the toys from the Toy Story series, they can't stay your heroes forever ... because they are deeply, deeply broken.