I knew better…

So my ex and I were together for a little over year. He was sober when we met and relapsed – with the drugs came the cheating. The relationship ended and a year went by with no contact. He reached out and we started talking again, he had become very promiscuous in the year apart and was still on this sexcapade which caused many problems because I was the one being rejected. We would talk and stop with months in between over a couple of years. He was arrested in March and had a come to Jesus moment proclaiming his love for me while in jail for 2 months and I fell for him. When he was released he couldn’t run far enough away from me. Leaving me with a cell phone bill and many ugly texts. 3 months went by with no contact again and he is arrested, again and like the last time he reached out. And yes. You guessed right proclaiming his love for me. There is a girl that he seems to always go back to and today I asked him to stop communicating with her and he blew up saying I’m controlling. She sent a picture of herself to him in jail. I’m not stupid and know she obviously has the impression he likes her too for her to do that. Why is it so hard to walk way when everything in me knows I should. He will never change and there will always be other women. My gut says block him and move on leaving him in my past but my heart still cares. Any suggestions??