Is the job enough to live on with universal credit and child benefit, though, and if you upped your hours? Plus have the equity on the house.
He is using the children now as a way of keeping you engaged and actually in some ways already punishing you. By being so melodramatic, he is making your thoughts turn to him and DS. In practice, there is probably nothing which thousands of parents all over the country need to deal with. Then of course, there is the stuff which is all about him (you are right, he needs to see his Gp and/or a counsellor). Remember it goes in the parcel you metaphorically leave on the table. Then pressuring you about what you are going to do about your mum, when actually you don’t know and cannot really know as it is a difficult situation.
So no wonder you feel anxious. You are not being wet or a victim (well, in some ways you are a victim and to be honest, so have many other people been from abuse and that is nothing to be ashamed of). Do not add to your burdens by negative language and beliefs about yourself. You are a person who is, in time, going to sort things out and learn and grow from this situation.
Regarding your brother, it is very difficult to comment on what you see in other’s marriages because at the end of the day, you do not want to disrespect their choices. I said to my sister something which I felt about her husband and with what I thought were her best interests at heart and it ruined our relationship. So I think your brother is walking a bit of a line by saying what he thinks (your partner is a bully) and that it is your choice (you are the one living with it and may not agree, although now you do). It is a risk to speak candidly about what you think of other’s relationships, unless they ask for advice.
The problem is, after many years of child-reading and without enough money, the idea that you should just leave is difficult to put into practice; plus with all the emotional manipulation and messing with your head, the extent to which staying is a choice is questionable- it is more like you cannot think straight because you are always responding to his needs and attempts to keep you engaged. Which are relentless and the only way to stop them, as you are finding out, is not to speak to him, or be in a situation where you are constantly putting boundaries around what you take on board as he does not respect boundaries. I suspect that your counsellor will be better than me at suggesting how to do this.