Oh hun, I'd love to tell you that he will eventually change but i've been in your situation and he sounds a bit like my ex. We split up shortly after my youngest was born & i felt exactly the same as you because i was left holding the baby (so to speak) I was the one who was stuck in every night 24/7 & he just left me to it and carried on like a single bloke with no responsibilities, going out, getting drunk, sleeping around.......................................I resented the fact that we both created the life but I was the only one left with the responsibility. I loved my kids but i did find being on my own without the support of my OH hard.
Hun, you are doing a wonderful thing, looking after your LO on your own is such a difficult thing to do - as is coming to terms with the fact that the father isn't interested. It does get easier over time. You have to accept that your ex isn't the man you thought he was and that he's immature and irresponsible. One day he will come to his senses and he WILL realise that he's lost out and then he's the one who has to deal with the consequences of that.
Try and make a bit of time for yourself so that YOU can have a life outside of looking after your LO and maybe your ex won't be such an issue. I know you want whats best for your baby but if he's not interested he's not going to make a very good dad anyway.