I still have strong feelings for my sort of "ex boyfriend" do I ignore it?

ok so i dated this boy last year from may to august, we weren't OFFICIAL but we were seriously dating.I ended it because I wasn't ready for a serious relationship and that's what he wanted. a month and a half ago or so i started talking to him again, i apologized for breaking it off the way I did, and explained that i wasn't ready for a serious relationship. and he forgave me and we started talking again, until a few weeks ago, he started talking about how he's been sleeping around at parties and such (he's 18 graduated from Highschool last year.) I got upset because it was like he was bragging about it. and we haven't talked since. I can't stop thinking about him, i miss how sweet he was, he was the best guy i ever dated. but i don't know how to start up conversation again, or even if i should. by the way, i know i should not be upset that he slept with other people, we weren't together, I KNOW THIS, but when we were together he was all "I want to wait for love!" I dont know, i know i shouldn't have gotten mad, so please don't scold me for it