What does he mean " I don't want nothin serious"?

well it sounds to me that the guy is looking out for his kid and also for hi feelings. I'm no father but I guess that if he loves his child it hurts to know that he may not be always there for her and also the fact that he is no longer with the momma well it might make him hurt too because he may have had strong feelings for her. So your move should be this. You may say that you like him a lot and want a relationship with him but I think its better to say " Hey id like to be there for you." That way he knows that you want him but that you also are giving the space needed for healing or adjusting. And another good thing to do is get a bit involve with the girl. I'm not saying like go play with her are act as her mother but more as show him that your interested and maybe do something to help him be there for hi child and stuff like that. You know the fact that he says he want nothing serious is not that he doesnt, its more like a I'm still hurt and need help healing first. So go for it girl.