Am I being cruel by breaking up?

I have been thinking about ending a relationship that has gone on for over four years. My partner and I have had our share of ups and downs, but it is his deteriorating mental health that makes me believe there is no future for us. The only reason I haven’t broken up with him yet is because of the cruelty associated with this decision. I know that he will never forgive me, but I also believe it will do him good for me to leave because it may finally push him towards getting the help he desperately needs. He doesn’t know I’m going to end this, and I dread the effect it will have, but I have reached a point where I am worried about my own well-being. Is this a selfish reason? Should I stay and hope he gets better?
If you know you don’t have the tools to cope with his condition, and he hasn’t tried to get help yet, this is not going to work because hope alone doesn’t resolve anything. If you are already aware that this is taking a toll on you, and don’t do anything to address it, you are making a bad situation worse because your ability to manage will be even harder. Do what is best for you first, because that puts you in a position to make a decision that will help you both. Don’t stay in a relationship out of guilt because it’s the wrong reason, and the inevitable resentment will make it hard for you to have any kind of friendship with him in the future.

A girl and I had a casual affair two years ago, and she has never reached out to me since. I have tried to contact her multiple times, but she ignores me. What did I do wrong?
This isn’t about you doing anything wrong. It’s about her making a decision about what’s best for her and choosing to have a life without you in it. Accept
her decision and move on.