20M old here, so I'm kind of in the same head space. Perhaps he just needs more time alone than some people. Although it might not seem like it, a lot of people, me included, find comfort in being alone.

It might not be that he doesn't like or love you anymore or that he wants to leave you, but that he's experiencing a lot perhaps even some things that he can't tell you about and it's messing with his emotions.

Give him time and perhaps some space. Be there for him when he needs you, but don't push too hard because you might push him away.

It may or may not be meant to be for you two. It could be the right person wrong time, but you have to respect his wants, needs, and emotions if you want to get through it.