I think the only thing you know for sure is that he does not love you. Make a life for you and your baby. Someone who loves you will come along eventually.
I can't say for sure that is what he was doing but it is very possible. He could have been scared of the pregnancy and that was his way of escaping was to run. It's not the right way but he may have just gotten scared. Did you ask him where he was for the last five months or what he was doing? I would start there and find out why he left for so long. If you decide to get back with him don't get into it too fast. Decide that this is what you really really want and let him know what you expect. If he messes up again then he's done. But again that's if you decide to take him back.