How do I move on when I don't even know what went wrong?

He obviously thinks he's better off without you. Maybe you were too controlling/jealous ... etc..?

Wow. I know that must be hard. So sorry. Even though you can not see it now. This really is a blessing in disguise. He has just shown you his true colors. And do you really want to be with someone who doesn't even have the guts to talk to you in person and let you know what's wrong. He is obviously a coward and has a lot of fear and this is his way of handling that fear by running away. Hoping it will all just go away. IF I were you I would write him a goodbye letter and end it from your side. You may never get the answer your looking for. But this is not the kind of man you want to spend the rest of your life with, afraid of the next run away. Again sorry and stay strong. Love yourself. And comfort yourself

There was obviously a problem and he didn't feel as though there was a point trying to work it out. Maybe he felt as though things would never change, or maybe the issue was that he wasn't happy and he found someone else. Whatever the case is, he didn't confront you about it like he should have. You will need a lot of time to get over something this serious, and you may even need to talk to someone or keep a journal to get all of your feelings off of your chest.

The fact is, is that he left and you may or may not hear from him. Try to get things straightened out and don't be dependent on a relationship to find your happiness.