Jenarry, I agree with whoever said this doesn't sound self pitying at all - it sounds like you have been through a rough time and you are only human. Life can be overwhelming at times and you need someone or something to lean on and help you through before depression sets in or a breakdown happens (I speak from experience, as I had one myself not to long ago, after letting things get on top of me).
Your son - I'm sure he's a brave little boy and diabeties, although very difficult and not a nice thing to have, is something he can live with. My mum has it and she lives her life and gets by, always has done. Just keep his spirits up, show him he can live a normal healthy life with it, and help him watch what he eats, exercise, etc. He'll be fine. It's not your fault AT ALL, so don't beat yourself up about this.
Your ex partner - well, he's a git and you're well shot of him. Easy to say I know but remember that if he isn't making you feel good anymore and he is more caught up in his girlfriend than his son, then you don't need him. I'm sure you will find someone better who treats you like gold in time. There are some 6 billion people on this earth and by the time he realises he has lost a good one it'll be too late and you'll have found someone else.
Just concentrate on yourself and your son and getting your life back on track and you'll be fine.
It you are feeling depressed or overwhelmed, see your doctor, there's no shame in it. I went on anti depressants and got some counselling on the NHS, it was good to have someone to talk to and just keep me afloat and I'm doing okay now.
Good luck hun.