What's the right thing to do?

I'm going to make a long story short. I was totally crazy about a guy I was dating, but he broke up with me, breaking my heart, and dated another girl. I was so hurt, I still have yet to get over it, even though it's been months, but I began dating a guy I had been friends with for years. He is so good to me, we match up so well and get along. It's just amazing. But I have to face it, I don't feel as crazy for him as I did my ex. Recently, my ex has come to me saying he wishes he could have made us work, and that he misses me. We attend the same church, so avoidance is difficult. He's flirting and I can't help but flirt back a little. But I'm tired of it. I don't want to have these feelings, especially when the guy I'm with is so good to me, he deserves my loyalty. Any advice on why I still feel so strongly for him, and not my current boyfriend? Or how to shake the feelings? Thank you!