Is Jason really competitive though, apart from with Matt? I thought he was just naturally talented at everything he tried his hand at/an overachiever because of his dad, which sparks Matt's competitive streak, which makes him compete with Matt because he threatens his superstariority and, by extension, his relationship with his dad. No one else is really a threat to his superstariority, so he doesn't have to compete with anyone else.

As for why he doesn't go for it in the first place, I think it's still a matter of having an image to uphold. Acting is for fags and girls, and if his dad found out he was acting (even the lead in Romeo and Juliet), he'd be given a stern lecture (or worse) on how to be a real man, playing sports and sleeping around/settling down with a proper girl (depending on his dad's view on women). Then there's what the rest of the school would think if they saw him acting. But being the superstar that everyone loves, he has licence to do whatever he wants and still be considered the superstar; something he wouldn't necessarily realise at first glance (possibly the actual turning point?). Plus, it's about man/woman love, so it's actually a pretty strong reiforcement for his heteroshield.