Answer to question #2 -
There are two kinds of divorces:
1) you jointly agree that you don't want to be together and somehow manage to agree enough to settle things without too much negotiation
2) one party wants to get the hell out regardless of what the other person wants or doesn't want
Run, don't walk to the nearest legal aid, recommended divorce lawyer or paralegal and get shed of the bum! The only permission or consent you need for a divorce is the judge's!!!
The way it looks - your ex has two women - one that he lives with and 'cares' for and one that he can take all his rage and frustration out on - that's you - even if it is indirectly through your son. Everything that you make, or save, or put aside in a retirement account that you are making NOW - two years after you've split up - he could be entitled to half of - and he can turn right around and spend it all on his new dame.
It's probably time you moved on, too, and into a better life for yourself. OH, and even if your face falls off, grit your teeth and don't give your ex tit-for-tat by criticizing him to your son. It's not for him, or for you - it's for your son. You might however, casually mention that while the both of you love HIM, you don't particularly like each other anymore and you will do your best not to put him in the middle. Then, just do it.
BTW - I've been married and divorced 4 times, had a long term live-in relationship for an 'almost' number 5 marriage, have two sons and two grandsons and a granddaughter. Not only have I been an optimistic with terrible taste, but i've had the opportunity to see how my choices have impacted my kids over a long term. No plans for a #6.....