There are a lot of pieces to that, but I ultimately realized that I had been suffering from long-term, chronic depression -- the kind where you're not necessarily sad, but the world just seems very... flat. And you are irritable a lot.
I want to recommend some things (understanding that I'm just trying to get you to think about them -- I don't know you, so I could be way off course... but). 1) Look into whether you have depression or not. At the very least, see a therapist. Maybe get a pyschiatric or psychological evaluation as well. Because depression sucks, and if you are battling it, you want to know.
2) Start looking at your life. What do you want out of your life? What would you hope for if you could "blue-sky" it? Because you need to make this life count... regardless of what your partner's expectations are. There are lots of books on this subject (random one: "You Are A Badass" by Jen Sincero).
3) Look at your spiritual life. (I don't necessarily mean religion.) If you are like a lot of us, it has kind of languished. But it's one of the legs of the stool, so you shouldn't neglect it.
4) Quitting is always an option. Telling yourself it isn't is just a way of locking yourself into BS options that may not work for you. Yes, there would be an economic hit. Maybe you'd have to sell your house. Maybe your partner would divorce you. It's OK to consider the drawbacks, but leave the option on the table, because... this is your life, friend. Destroying it for money is a bad, bad plan, and will teach your children the worst of lessons -- that life is a horrible grind for security, despite the fact that we hate our lives. Bad, bad outcomes come out of that lesson.
Take what you like, and leave the rest.