Kk I actually read your post. Yea that's pretty heartbreaking. Ignore what the other guy said about finding a rebound.
As a guy in a long distance relationship, I understand what your ex means by saying he wished that he treated you better. I always feel that way when we're apart - and I feel like I do better each time we get back together - but you feel that way when you miss someone, not when you already have them there. This is likely why he didn't try harder during the relationship.
I stand by my previous advice to get a new hobby. Go running. Pick up rock climbing. Meet new people - this is a new chapter for you, and you have plenty of opportunity to learn. Put yourself out there and distract yourself, otherwise the thoughts will consume you in waves.
Many of us are commenting from experience. Breakups happen. But they give opportunity to grow in a way that you haven't grown before. You have newfound time to be alone - time previously spent with him. Do something with it.