My ex broke up with me but now he wants me back. Problem is, I've started "kind of" seeing someone.

I started dating this guy back in July/August 2012. We had a lot of fun together but he always told me he wasn't ready for a relationship because he was scared to get burned again. He fed me the story of how his ex hurt him, etc. I bought it. I tried to ignore the fact that his heart was still partially taken by his ex while I was so deeply in love with him. He told me he thought the world of me but he felt pressured the one and only time he said he loved me. He was more about sex than anything because he never would have me as his "girlfriend" just the girl he was dating. No titles. We were off and on a lot. All of my friends and family say it's a bad idea but he wants me back. He told me he didn't realize what he had until she was gone (me) and that he misses me and his kids miss me. I loved his kids as much as him. I cried so many times though and he was so mean some things. We never fought but he just is crazy. He has a bad temper with people that make him mad. I loved him with all of my heart and still care about him a lot but I'm finally getting over him and he is trying to win me back now?! I don't know what to do. I ignored his texts of "I miss you" for a week. He finally made me his girlfriend only to get another girl the next week. Then we finally broke up and I didn't hear from him for over a month or more. Now, he is telling me he misses me and all of what I said above. He said he would do anything for me and he wants me back really bad, he will make things better than ever, let him take me on a date, etc., then he says (after I ignored him) that he misses me and will love me always. A word he said to win me back last time but not to this extreme. He's never acted like this before, but then again I've never resisted this hard either. He left a note on my car at Wal-Mart in the rain, after he went inside looking for me and couldn't find me. He is not giving up and Idk what to do. I don't know that I want him back. I don't want the heartbreak again. I've started talking to a new guy but it's a complicated situation too. He's completely different from my ex though. He's really nice and he cares about me too but of course he doesn't love me yet. He's one of my very best friends though. I've known him for about a year and a half and he was there for me through all of this mess with my ex. I can't just end things with my new guy to go back to my ex with uncertainty. But, he isn't giving up!! I've tried to make him quit texting by ignoring his messages but he keeps going. I love him still but I'm scared to go back. I really like the new guy and want to see where it goes first. As bad as it may sound, I want to try this new thing first, and if it doesn't work then we will go from there. But, I know that if I didn't have a new interest, that I would be back with my ex in a split second. It was so hard to get past it and I was just topping the hill. I don't want to go backwards because it's too hard to get past over and over again. I don't know what to do though because I feel like he's sincere because he's never begged me before. He's never gone out of his way to make sure I knew he cared. He hasn't sent flowers, etc. but he did put a note on my car and he's texting. I know this is rambling and I"m sorry. I just need advice!