You need an exit strategy. You probably think you don't or that you cannot afford it, but make your plan a longer term goal, 2-6 years. Get a separate account at a different bank and start saving. Get the baby weaned and yourself in a job. Make your plan. You don't have to leave him, but you knowing that you could leave whenever you wanted to leave will give you your power back in this relationship even if he has zero clue about your money because you will be different. You will feel better. Don't get mad, get the money.
The money he spends going out with the boys, you take the commensurate amount from his pool of funds, or the household's and put it into your private, separate savings account. It's a good way to start off your savings.
Remember, as you save money, no one, but no one, needs to know. Nor should they know, not your family, not your friends, not even your bestie, not some women's group, not your therapist, kid's teacher, no one. Do not spend it in a way that anyone would question you about it. This is your money and nobody else's business. If people know they will either spill the beans, probably while drunk in a group setting, and/or try to borrow it from you.
Stop telling your mother-in-law ANYTHING about your relationship that is not sugar and light. What she does for your family is because she is his mother and their grandmother. She is not your friend. Repeat that to yourself whenever you feel the need to confide in her. That woman is not your friend, she is his mummy.
He doesn't want to be there with you and the baby. He couldn't have been clearer than if he took a bullhorn and fitted over your ear, and at the highest volume shouted "I don't want to be here." Mummy has given him permission. Sugar and light are your best weapons, if he wants to go out, don't object, save the equivalent amount of money. If he is entitled to it, so are you.