Broken engagement

My ex fiance and I were together for 2 years and 3 months before he proposed to me. Our relationship seemed great. We had our occasional disagreements and were able to talk through them. I felt like he was the one. In December, I brought up something that has been on my mind about how I wanted to find a way to feel included in raising our kids Jewish (I'm Christian he's Jewish). He seemed freaked out that I was having these thoughts but then he seemed ok because we talked about seeking counsel from our friends and the rabbi officiating our marriage. Well, the morning after he was acting weird and went to his mom's for the weekend. That whole weekend he didn't want to talk to me and said we would talk when we got home. When he got home, he broke up with me. He said he wasn't feeling confident going through with the marriage. When I asked him if we could put it off, he told me he didn't think we could bounce back from the broken engagement.

I moved out of his place the end of January. We talked a little after the breakup and he told me that he loved me but we weren't right for each other and we had different needs etc.

My question is, why would you propose to someone and in the face of conflict, decide to give up everything? I also can't believe he would say we aren't right for each other when a few weeks earlier he was saying he was looking forward to having kids with me etc.