Could I be making my mental health worse?

Talking with a friend of mine about my issues, he told me that I should stop saying "I'm a piece of shit" and that I have a shitty personality to myself. He also said, that I'm a good person despite thinking that, and that I should have more confidence in myself and in my actions.

Now, sometimes I realize I do this and just bring myself down even more. And the thing is, I don't know the reason behind it. I make sure I isolate myself and not talk to my friends, (it has been months since I've last talked to my "best friend") and actually portray myself as a mean, bad person. I guess he said that, because I act in an awful way towards him. I guess despite everything I do deserve to be alone.

What my "question" is, could I be making my mental health worse by acting this way? Is it some sort of coping mechanism? Or am I just a toxic, awful person with no chance of redemption because I just spiral down into worse places?