I'm going to cancel my trip to see the man I am interested in because of his mental breakdown.
What is your reason for this?
I find him bad for my mental health.  He's a drama king.
It's wrong to cancel plans that you both have made, since your partner was planning on seeing you.  You should be ready and willing to support him if he is having mental issues, since you would expect the same thing in return.
I'm not heartless. I do care about him, but I can't support his situation.
I'm sorry you are feeling this way. It's wrong to cancel a trip you have planned but you should try and support your partner during their mental issues. This is the time that they need you the most.