I'm really sorry that you're going through this. Living with an alcoholic downright sucks, but the emotional backlash of splitting up with them can be enormous. I've been there, and done that, and I know how disorienting it all can be
It's great that you're thinking about what you want from life. I'd recommend you also think about that in terms of the things you have control over and/or can influence, and the things that are other people's responsibilities. Him admitting his role in DS's emotional issues is not something you can control or something that is your responsibility. You supporting your DS and helping him to understand that it's not his fault is something that you can do.
One of the big problems in being in a relationship with an alcoholic (apart from the unpredictable roller-coaster ride of calm to drama, peace to chaos) is that the non-alcoholic gets drawn into the alcoholic's problems. It's very easy for us to end up feeling responsible for doing things that we feel will help them to realise the problems their drinking has caused, or for us to make choices that we think will influence their decision to drink again. While that's a very easy trap to fall into, it's massively counter-productive. It means that our attention is on them and their drinking, rather than on us. Al Anon is great for helping us to crow-bar our attention off of the alcoholic and back on to us, where it belongs. Melody Beattie's book "Co-dependency No More" is very good for that, too, although it might be a bit tough reading right now as she doesn't pull any punches.
One of the hardest, but most liberating decisions I made after I split up with my alcoholic ex was to decide that any decisions I made were to be in my interests, and/or my children's interests. If that happened to coincide with my ex's best interests then, great, everyone wins. If those choices unfortunately inconvenienced my ex then, well, so sad, too bad, not my problem.
You will get through this. It will get better for you and your children. Keep your contact with your ex to the absolute minimum and don't bother arguing about who did what to whom, where the blame lies, the what-ifs and but-maybes. The only things you need to talk to your ex about right now are child contact and money. As for justifying yourself to others, the line "I don't wish to talk about this right now" works, especially if you just repeat it in as bored a tone as possible.
You're going to hurt and that's sad but that's just the way it is. You will feel better. You really will. You'll start to notice you have short periods of feeling ok, and then over time those short periods will get longer and more frequent, and then one day you realise you've had a really great day. Your children will be happy and relaxed, and you'll look back at your relationship with your ex and wonder why you stuck it out for so long.
Finally, I'd suggest you read this. It's from an advice column that is, funnily enough, written by an ex-alcoholic. He sums it up very well.