I feel like he owes you an explanation so you can get some closure. Can you ask him to tell you why he left you and tell him it will help you move on to know that?

As for going out with other guys, you don't sound ready for that to me, since you are still wondering about the other relationship and it hasn't been long. Are you ready to go out with other guys? Only you know. I think you need some time to figure out what happened, and if the relationship is indeed over for good, you need some time to grieve the relationship.

I'm sorry you are so sad. I hope he can give you an explanation. I think it will help. Good luck.