My partner upsets me, and acts single?

I have a 7month old baby, me and my partner were living together until one day he decided to leave he said it was because he couldn't cope with my up/down moods, but I found it very difficult as I suffer from postnatal depression and he never seemed to be there for me or understand, I've stayed with him when he left but he's just living like he's single, he hasn't payed anything towards our baby and he's out every weekend, he really upsets me, one moment he says he realises he is wrong and he cares about me, and the next he's saying he wishes I wasn't the mother to his child, it gets me really down, I keep thinking I can do it by myself and to be by myself and I know I will cope, but I love this man, I have a child with him, I just want him to change and step up to his responsibilities, he is one of the reasons I feel depressed, he doesn't answer the phone to me when he is out, and he says he wants to move back but part of me doesn't know if it wants him back, but then I don't want my child to grow up without a dad, I feel like I must of done something so horrible to him for him to be so nasty, one moment he's lovely the next he isn't, and he says its all my fault, I don't want him, but I don't want to lose him, and at the moment I contact him everyday just speak to him, but I don't no whether I should leave him be for him to get in touch with me, apprently if a man wants you they will chase you, but I'm scared of being on my own, advice please.