What should i do with the father?

this is a very long story but il keep it short.

i was with someone called 'Sean' for over a year before i got caught pregnant. All way though pregnancy he said he wanted the baby and me. Came 10 days after he said he never wanted the baby and never loved me. We then (stupidly) slept togather a couple times after we broke up. We ended up basically being bf n gf again without the status.. with me also having emails off all his friends saying that he was stil in love with me. We had a big bust up and he nearly left the country, and confessed into doing all sorts like drugs, drinking, sleeping with under age people.... it just gets worse. All this time he was also suggesting to give him space and then give us a second chance, so therefore leading me on. Either way it had been on n off, all along messing with my head to where i stood with him and our son. i never got any financial help because he didnt work at the time but agreed when he did, he would start. 10 months down the line he had an affair with a woman, ended her relationship and the poo hit the fan. He has james every weekend because ive never stopped him seeing james BUT now he has this new gf they get drunk everyweekend, whilst hes in control of my son. walking him up on new years day at midnight to take him out in the cold without a blanket too, and he was very very drunk.. Proof is there due to his facebook profile pic! his gf has a little girl and shes being put into the same situation too...

Im concerned whether to let my son see his father now that sean has no sense of responasabilty now hes all loved up. My main concern is my son and i dont want anything to happen. Ive tried talking to him but alas he refuses to talk about it saying im over reacting! His name is on the birth certificate so i dunno where i stand either. Financially now hes working, and refuses to help instead to buy the stuff.. which is fine by me but i wanted to see reciepts but got the response he wanted to see MY reciepts!! Any help would be amazing thanks im stuck in the middle here :((