You don’t really want to leave, you just want to shock him into acting correctly and let him know that you can leave if you want to and that he needs to start appreciating you.
Book a hotel and tell him that you’re staying out tonight.
Perhaps have a chat to the 12yo and explain (in kid terms) that your dad regularly has nights away and you just want one too.
Go out with friends or get a bottle of wine and room service and slob out in your hotel room.
When you get back I think it would be worth having some couples therapy.
Either you’re not communicating your needs properly or he’s just not listening.
Gently, this is why I would never be a SAHP because some women are seen as not as important by their partners.
Perhaps look into what career you will have when your youngest starts school.
You could think about doing an online degree or something.
Your life revolves around your DH and your kids, which isn’t good.
You are your own person and it’s time you had a social life and work towards a career of your own.
You have quite a large age gap between your kids. Was this planned?
Has his behaviour changed since having the second one?