Why can't me and my ex just leave each other alone?

We've been through so much together and it's like we keep finding ourselves getting back intouch with each other. We've cut each other with words we've promised we would never talked to one another again but it's like we can't leave each other alone. My life doesn't seem right without him but it's not perfect and sometimes added stress when we get back intouch with each other. Is it because we really haven't moved on and tried to meet new people or could it be true love I've find my self talking to other guys but it's just not the same and he implied the that he has talked to other women and it just isn't the same. I love him unconditionally despite what he has done and the hurtful things I've said to him and I ask myself if I was to meet the man of my dreams will I still feel this way about him or is it because I haven't met anyone that I feel really loves me for me and is it loneliness that is making us both run back to each other. I know only I could probably answer this question but I would love some input