Look up hoovering/reverse hoovering. Cut every avenue of contact. While ever there is one open you will just keep beating yourself up about him not contacting you. Don't give him the chance then you don't need to wonder.

It's not about being prettier or smarter or better than the women he leaves you for. It's about who is the best N-supply.

Maybe he is one of those that likes people he considers lesser than him so that he can feel superior.

He probably will contact you again. When the women he is with either runs down or gets jack of him he will come back to you because you have proven time and again to be a solid source of supply.

Don't give him the chance. The best revenge for this sort of person (and luckily the best thing for you too) is to ignore them.