I stopped him and asked him what was in his nose
Did you ask him to ensure that he is taking care of himself?
Yes, I care for him. I always want him to be healthy.
It seems you asked him about his appearance out of concern. It's okay to want someone you care for to be healthy.
He's such an asshole. He said that I should mind my own business.
It sounds like he has something to hide. You should talk to him again when he calms down and confront him about his uses.