Welcome to the community here. It does sound like your partner is going through a rough time right now for some reason. If he is unwilling to go and seek help, there is little yo can do about that unfortunately.
You mentioned there has been no contact and you are concerned. Do you have mutual friends at all? Do you know if anyone has seen him or heard from him?
Would you feel comfortable sending a text message saying something like "Hi. Thinking of you. Hope you are okay" and leave it at that.
Do you have friends of your own yo can go out with and spend time with? You also need to look after yourself in all of this.
Both my husband and I have mental health issues. I know I can be a horror to live with at times! I try to get out of my husband's way when I feel awful. I do sometimes go out for the day, but I let him know and have my mobile phone so we can keep in touch with each other as I know I worry him at times.
We can not change the behaviour of other people no matter how much we love and care for them. It may come down to you deciding if you want to continue with this relationship or let him go.
Wishing you well as I know that is not an easy decision to make.
Cheers from Dools