It's really hard being the 'defauilt' parent, isn't it? I have a bit of resentment myself in that I need to make special arrangements for childcare or for H to be in the house so I can go out at night and GAL, but the assumption is he's a free agent and can do as he pleases unless we specifically arrange this otherwise. I've tried to raise this with him but it hasn't been successful.
What has helped is for me just to imagine that he's totally out of the picture - that he doesn't exist. I make my own plans, arrange my own childcare, and if he does agree to take the kids, I always have a plan 'b'. I don't think he likes that much, but short of stepping up and collaborating with me more fully, that's the way it is. It has helped.
Most of my GAL is with the kids though. We get out and about to all kinds of new places and it doesn't cost much. We've had walks and picnics and trips out to museums and all sorts. I see my friends during the day when they are at school and invite friends to come and see me in the evenings when they are in bed or occupied on their own projects.
As you and your H live together, I don't think there's anything wrong with you just informing him that on thursday night, or whatever, you're going out between 7 and 10pm. If you believe he is safe and trustworthy to look after his children, I think it is perfectly fine to assume that he will do that 50% of the time and that you will have free leisure time as he does. He may well accuse you of abandoning the kids and he may well sulk and give you the silent treatment. So what? He's an adulterer. What does it matter what he thinks of you taking some time for yourself and leaving your children in the care of their loving father?
