First, four months is not that long to be into a breakup and I think the feelings are pretty normal. However I also feel like you may be spending so much time and energy trying to win him back and convince him that it’ll work that you’re not really giving yourself a chance to work through the actual feelings from the break up. Or to give yourself a chance to move on. There is the possibility that there is a better relationship out there for you. If that’s the reason he left and he’s never once considered reconciliation then I think it’s safe to say there’s more to his side of the story than that. Whether you know or will ever know is not all that important. As hard as it is, I recommend that you cut off all contact with him. Definitely do not beg him to come back, try to convince him any further that you’re the one for him, etc. If he decides he misses you and wants to get back together he knows how you feel and he can contact you. You can then decide if that’s something YOU want. In the mean time, work on being truly happy alone. Don’t necessarily date if you’re not comfortable doing that yet. Take time to figure out what YOU want, what YOU need and what YOU’RE willing to accept in a relationship so that you are prepared for the next opportunity.

Just my 2 cents. I know it’s hard as we tend to build expectations and plans that seem hopeless when a relationship ends. Try not to think about it that way, try to see this as a chance to get to now yourself and build a relationship with you that will allow an even better romantic relationship in the future!