How do you deal with partners with mental health issues?

I really need help on how I can help my partner whom I love to death and but can't leave him because of his problems. He gets depressed often and once he does everything become black and he can't do anything right. He would stay in his rooms for weeks not going out. He constantly reminds me that I'm the love of his life and the only things he wants in life and I feel the same but I don't know what to do. Currently, he doesn't wanna go to the hospital and I don't wanna force him, I can't in the first place but I don't know wht to do.