You’ll leave him at some point. It might be a while though as you will stay and keep trying to make it work first. That will be a miserable time for you and you will likely regret how long you wasted there with him.
When you do leave, and get your shit together, he will then resent paying maintenance to you and you will forever be, in his eyes, the awful ex who “shafted” him financially.
He will happily be an every other weekend day, won’t fight for more, and will enjoy his free time whilst seeing himself as father of the year.
While he is out on Saturdays he will probably get either his mother or a new girlfriend to look after his DC.
You, I hope, will look back and wonder what on earth you were doing but will just be glad that you grew up and out of that.
You will probably go on to marry an adult man who treats you with respect, and you will appreciate him all the more for that, and you will have a happy life.
Occasionally you will look at your ex, in ten years time, and have a moment where you realise what your life would have been like if you were still with him.
You will shudder briefly, and then smile politely, finish the handover small talk and then get back to your actual life.