I once had a roommate, that I would've considered one of my best friends at the time. There were 4 of us living in a house. He came to us one day and said that he needed to move back to his parents house for financial reasons. We told him that was fine and within a few days we had another guy wanting to move in, in his place, so no big deal. A week or two later, he moves out.
3 days later our internet and cable through Time Warner gets shut off. Well each of us had a separate bill in our name. Each month we would give each other money to pay each bill. One of my roommates and myself go down to Time Warner to see why our shit is shut off and to put my name on our bill. Well it turns out this guy that moved out a few days before had just been taking our money and not paying the bill. This went on for months before they shut us off. Our regular bill was a little over $100 but over $700 was owed and they wouldn't turn anything back on until it was paid.
Naturally, we got on the phone with this dude and had a huge blowout. He eventually paid us all back the money we had given him for Time Warner all those months. But he was essentially dead to us.
Years later I was playing in a 7 v 7 soccer league he was in. Different teams. Slowly we started chatting, and eventually I told him I was over what he had done and that he and I were good in my eyes. However, some things you just can't go back on I guess. We never became friends again, which is fine. I haven't seen or spoke to that guy in over 10 years.