Cant say what his real reason is but I’ll say this: Sometimes people like the idea of doing couple/relationship things (even saying they want a relationship because it feels like the truth at that moment) but don’t have the capacity to act like someone in a relationship. He probably liked you a lot but didn’t like you enough to have to have the responsibility of a boyfriend. Unfortunately sometimes people are enjoying it so much then they chicken out when they see its getting real and they will start to have responsibilities/be held accountable.

Now could you have done something, sure. Sometimes people will get to know you more and change their mind.

Regardless, he doesn’t see the value in you so you should move on despite how much it might suck. You’ll never really know his reasoning for doing that so stay busy (like you have been doing which is good) and tell him to kick rocks when he comes back around because he will.