He left me without an explanation

A month ago my ex bf contacted me saying he missed me. I felt bad that he was feeling a certain way so I forgave him and let him back into my life. A few weeks later, we continue talking and I begin to develop feelings for him again and I think he did too.. He'd always comfort me. He'd tell me that I'm perfect and that he'll be whatever I wanted him to be. Recently he cut off all contact with me and didn't even tell me why. I just can't help but think he found someone new or that I did something wrong.. what can I do to forget about him and move on with my life?