There is no type of mental illness that "makes" a person hit another person. Bipolar disorder and other types of mood disorders/anger management disorders can increase angry feelings, but they do not MAKE a person hit another person.
If you believe that he cannot help himself when he hits you, then you are enabling him to hit you. He CAN help himself. There are other ways to express anger. If you love him, you will do what it takes to help him learn those other ways. And that means getting out of there. And taking the kids with you.
Your kids also need to know that its not okay to hit other people. Your kids need to see that Mama sets a firm boundary around hitting, and will remove herself and them from any such environment.
And lastly, most importantly, there is NO CONDITION under which it is okay for you to be hurt like this. He can kill you or cause you brain damage by hitting your nose (the bone there is sharp and can be fairly easily driven upwards into your brain).
Get out of there so he can see how serious his behavior is, and be motivated to change it. You can still love him, you can still go to psychiatric appointments with him, you can still talk on the phone with him, you can still be supportive you're just doing it while also keeping you and your family safe.
Hopefully he will find the right combo of medications/therapy and you'll be able to be together as a family again. It might take a while, but it will be worth it, and in the meantime, the damage done to you and your kids will be minimized while he is getting better because you are not available to be hit.