I dont really know where to start I am 90% sure I want a seperation.

I accidently fell pregnant to my partner 3 years ago and have a lovely boy out of it. I never intented to have children with him as then he was messed up (drug addict) and basically the complete opposite of what I believe in and I could never figure out why I loved him but I did, We got married over a year ago and I felt like I shouldnt but I did I thought it was just nerves but now I think it was because he asked me for the wrong reason (he told me one night he didnt even love me when he asked me)
He barely helped me with our first son and when I got pregnant with my second I hated him, I was working, tired and sore and he still never helped and I used to wish I wasnt pregnant and then I would feel horrible for thinking that about a beautiful baby.
My main problem is how he talks to me, he talks down to me and he calls me names - especially after a few drinks and he drinks every day. He seems to be a cranky man as he just loses it. I have asked him to leave numerous times and he just says he wont. He told me once if I left he would take the kids - I said why you dont know how to look after them.
I feel like it is domestic violence when he talks to me like he does but then there is days when he is so nice and I think I do love him. I am just so confused, I cant talk to my family as they just dont understand and are EXTREMELY opinionated and then I feel like I have no one - and no where to go, I dont want to go to my mum because when she is around my children she takes over and has no routine and I know she is doing it out of love but they are my kids and I am the one that knows how they work.
My husband is a type one diabetic and I fear that he is going to have a heart attack or something will happen, he has hypos all the time - and when he has them he is rough and rude and horrible and I told him I feel like not helping him and leaving him to die and I should never feel like that its not the person I am. Of course I always look after him. He smokes and refuses to quit so he is going blind in his eyes - and that is what makes me fear a heart attack,
I fear that if I did leave him if he was having my kids that he would have a hypo and hurt them or ...just not wake up .. That is another thing he sleeps so so so much and I have left him with the kids and he has slept through the baby screaming so I dont leave them with him anymore.
I have gone back to work as he refused to keep paying bills and he doesnt understand my argument that he obviously has enough money to as he always has beer and he plays golf. I dont mind going back to work I just hate that I have gone back to a job I hate.
I want to leave as he said he wont - I feel like I want him to be cival I want to be friends for our children and be able to trust him with them.. I know that he loves them but I have said that if he loves them he would leave because we cant have this sort of relationship around them,.
The worst thing is I get so tired and so mad at him that I take it out on them (yelling) and then I feel like the worst mother in the universe.
I could probably go on and on I guess its kinda obvious what I should do but why do I feel like I love him and like I am abandoning a lost puppy or something (when he is nothing like that)