Op, reading your first post, was like reading my life. I would have thought your DP was my ex except the timing doesn't work, and his new wife doesn't have any children from previous marriage.
We got together when DS was 2, he was wonderful, there were a couple of things I was not happy with when DS was about 6, we discussed, he behaved, pretty much, or so I thought.
When DS was 8, we moved. I got pregnant, couldnt take up a new job. Lost my financial indipendence, left all of my family and friends behind. But you know, things were ok, we were getting on, Ex was being a good dad and a good partner as far as I could see.
When DD1 was born things should have been perfect. It actually went down hill from there. When DD1 was nearly old enough for nursery, I started looking a college course, aiming to start a new career. I got pregnant again, unintentionally. The glimmer of indipendence went out. All the while his behaviour towards DS got worse and worse and worse, I felt utterly trapped. I couldn't see a way out. The friends and family that I occasionally got to see all thought he was a great guy. DS accused me of making things worse every time I stepped in to defend him, which I did repeatedly. and even though I knew it was wrong, I couldn't see how wrong because I was in the middle of it, and I didn't realise how utterly under control I was too.
DD2 was 2 when he finally left. 12 years in total that man was 'dad' to DS. He turned him away on his doorstep when he walked to his house with DD's to visit. The very worst thing, was that DS adored him, he did everything he could to get praise and recognition from him, because as far as he was concerned, he was his Dad. And ExP did just enough nice things to keep DS loving him, and thinking that it was all his fault when Exp was vile.
I have spent the last 2 1/2 years, with the help of some amazing professionals (primary mental health workers, social worker, children's outreach worker form WA, WA support worker, Health visitor) trying to help DS work through some of the shit that EXP put him through, a lot of which I didn't know about, as it happended before it even appeared on my radar of things I was unhappy with, some of which I knew had happened while i was desperatly trying to work out a way of getting out of the relationship, but didnt know how or where to turn, and before I found MN.
The things that you have described are EXACTLY the kind of things my EXP would have done to DS shortly after DD1 was born. It got MUCH worse as DS got older and his hormones started raging. Don't wait. Please.
And if you do LTB, watch your back, because in my experience they absolutly get worse when you think you have got rid of them, especially if you have children together.