First of all, your English is not bad at all so don't apologize or worry about it. Second, I'm not intending to sound mad, this is a discussion among fans- I probably sound harsher since you can't hear my tone of voice.
Anyway, it's not that I think Leo can't get better. The problem is Leo doesn't believe in getting help because he's stubborn and proud. Yes, it's true that in Jenna's route, he at least admits his faults and that's important.
You used PTSD as an example. People who learn to manage their PTSD get professional help and at some point admit they need it. While Leo doesn't have PTSD (some people think he's a psychopath but I disagree with that too), he hasn't started with the important step yet and that is admitting his troubled behavior is a problem he can't deal with on his own. Maybe he will, maybe he won't.
I can't see how Leo could ever have a healthy relationship with Chase, given that Chase is the reason Leo went insane. Even if Leo got help, it will never be the same again. Especially in Jenna's route so far, where Chase is developing feelings for Jenna and is now put off by Leo's toxic behavior. Chase doesn't give mixed signals anymore. It's sad but they won't work and forcing them to work is wasting the point Leo's route was trying to make.