First of all, I am very sorry that you are in this situation. It totally sucks.
A liar will not stop. At some point, I predict you will tire of being treated in this way and probably want to leave. His denial is not helpful, but a bunch of apologies, remorse, and empty promises don't really help as much as you'd think. I encourage you to leave for your own personal emotional health. That said, you probably cannot just leave today. You need to think carefully about what you can do to be able to leave ... put some money aside, possibly get higher paying work, line up social/emotional support (especially given your SN child), identify where you will go, etc.
It is a lot to think about and you don't have to do it all at once or even this year. But start thinking in those terms and putting yourself in the position to leave. If everything works out and you no longer wish to leave ... you have lost nothing. All women should really have an exit plan of some sort even if they are happily situated, because as you just found out (and as did I recently), things change and/or are not what they seemed.
I wish you the best. Hugs.