While he has never been physically violent, he is mentally ill and refusing to take responsibility for it. He keeps guns around the house, not secured safely, which I am not okay with. He is patronizing and tends to ignore me or roll his eyes at me whenever I do or say anything he doesn’t like. I have suggested couples counseling, but he refuses, and every attempt at conversation is shut down.
By far, the biggest issue though, is that I have just realized that this is not someone I want to date.
Unfortunately, our lease still has several months to go, and neither of us have friends or finances available to make moving out a viable option.
I am tired of this relationship, and it is exhausting me to keep up an act that feels disingenuous, and I feel cruel misleading him, though I can’t imagine he doesn’t have some idea, and is 100% happy himself.
My fear is that, were I to end things, he would become, not violent, but highly inconvenient to spite me.
I worry that he would intentionally create messes and refuse to clean them, or refuse to pay his portion of bills.
I feel stuck staying in this relationship that is making me miserable, and I don’t know what to do.
Your situation doesn't sound like a fun one. It's unfortunate that you are only a few months into the lease, and that you moved in with someone you've discovered you don't want to be with. My first thought is, maybe there is something you could work out with your landlord, some sort of agreement? They might let you switch out with someone else if you can find another roommate for him. Or maybe you can just get another roommate if you won't go above max occupancy.
The problem is that you are facing relationship and living situation issues at the same time. But if you don't want to be with someone then you don't want to be with someone, and your living situation is the second issue to deal with.
Your fears may be merited, but it's hard to say how he will react to the breakup. If one person in a partnership ends things, it's over, so it's not like he can say no to the breakup. He may be immature or rude about things after, and given how he has acted so far it's understandable you're concerned he will be a real treat post-breakup.
Try your best to be civil about things and try to make some agreements about the living situation after the breakup. It might be impossible to talk to this person, or maybe he'll be surprisingly willing to agree to some new ground rules. He may have some of his own. You can make decisions about who gets to keep what stuff (I would not be picky about that), who will keep sleeping in the bed and who will take the couch or floor, and if you can it might be a good idea for one of you to change your work schedule so you two aren't around each other as much.
You will ultimately likely have to pay the rest of your lease, but maybe you can minimize the time you spend in that environment. Maybe you have a friend or family member who will let you spend more time over at their place, and crash there sometimes? You could just get out of the house and do other things more, or spend more time at work. If you don't have much of an escape from home, then at least maybe things will be civil enough that you'll both be able to do your own thing while you're both stuck there together. Maybe you'll even be able to continue dating other people if you want, but I'd advise you not to move right in with someone else after this is over!
I hope this is helpful. At least he isn't abusive. If that becomes the situation then I would get yourself out of there asap!