I might have missed this but you can formally separate whilst living in the same home as your stbxh and claim universal credit. If your home is rented you can presumably claim for half of the rent and consequently separate your finances.
If you can't work additional hours because you no longer drive 'his' car, why is that his car? If it was bought whilst you were still a couple then it is a joint marital asset and half yours. Did he pay you half of the value? If it is on finance and there is equity in it then he should have paid you half of the equity and essentially bought you out of the car. Only if it is leased or provided by his company would it be entirely his car.
You need to think about this practically. You have x amount to pay for your half share of the rent and y sum for 50% of the bills, get in touch with the benefits office and make a claim for support based on your wages. You should also need to claim child maintenance from him your labour is as valuable to the family as his.
He is using his financial power to hold you in an untenable position basically to punish you regardless of whether that if understandable or not due to him feeling betrayed.
He has to be made to realise that you are no longer his wife and he cannot control who you see or what you do. The more financial control you take over your own life the less you will feel beholden to him because he pays for everything.
You are not the first person to break up a family, there are a million and one reasons why relationships break down. Just because yours was due to realising that you are gay doesn't mean you should have to be punished for evermore.
Pp's are right he is not acting in the DC's best interests. If he were he would have sat down with you discussed the practicalities of the situation and come to an agreement as to how to move forward. He's had a full year to come to terms with this situation.
No one likes to be cheated on or even feel that they were cheated on but most adults will experience this at least once in their lifetime and they learn to move on with life and see that things change.
His demand that you keep the status quo going for another 3-4 years is unrealistic. Can I ask whether you are still doing all the other 'wife work'? Does he wash his own clothes, make his own dinners, clean up after himself and do half of the general household work? If not they as I said before your contribution towards the running of the house has to be treated as important as his job and earned income.
Perhaps sit down and make a list of everything you do that benefits everyone in the household and how long it takes and show him precisely what your unpaid contribution to the running of a home is and how much it would be worth if you were even paid minimum wage for it.
I'm fairly sure you have probably kept up your role as main childcare cleaner cook and chief organiser throughout the year so as not to rock the boat anymore. He has to be made to understand that your work is worth as much as his, many people really don't appreciate just how much value this adds to everyone's lives and how much it would cost to replace it.
You should also start separating your time, you are no longer a couple you are to cohabiting parents with separate lives to live. He can't call all the shots just because he earns more money.
If you stop facilitating his life then I would imagine that he will realise that him moving into another property nearby and seeing the DC with a properly agreed schedule would be the best for everyone concerned.