I lost my best friend but I deserved it.

When you lose a friendship it means the friendship had some growth of some kind. Either you grew or your friend grew. In the first case my friend grew. I was toxic and wanted a relationship and my best friend did not. This was in highschool. Five years later, we're friends again because said best friend reached out to me and we've both grown. I've also left a different best friend behind. I found she did not care for her health and was racist, ableist, and I didn't have the time to try help undo that shit for her when she didn't want to.
Friendships change it's part of learning and growing to be better (or worse) people. Admitting if you were in the wrong and trying to grow is what keeps life better and meaningful. Otherwise you'll be stuck in a past (or a possible future) that isn't the reality of now. Only reality and now will help you.