<human>: My FWB and I have known each other for over a year. He's been there for me purely as a friend for most of this, listening to a lot of my problems, giving me advice. He was one of my most trusted friends.

Recently, I broke up with my ex. Not long after this happened we got intoxicated and confessed our attraction. We slept together shortly after and continued to do so for a few weeks. We never had a conversation about the boundaries or expectations of our relationship. I just assumed it was casual.

After about a month or so he stopped replying to messages, if I went to visit him like I usually did he wouldn't answer. We work together, and would only speak if I went out of my way to do so. I kind of felt like I was wasting my time so just resigned our relationship to friendship and got on with my business.

After about 2 weeks of this, we end up meeting at an event and talking about what had happened. He has chronic pain and had been on medication during this period, and he explained that this was why he acted the way he did. We slept together again.

So the problem is, during the 2 weeks we weren't talking, I went on holiday, got drunk and slept with someone else. Nothing serious, just bad decision making. Of course I told my FWB, but it wasn't until after we'd slept together and he was furious. He now wants absolutely nothing to do with me. I understand why and I feel shit for making him feel this way. We just had no definitions as to what was happening and I thought our 'thing' had naturally run its course. 

So my questions- was I terrible for acting the way I did? Do you think our friendship is repairable?

Can you give me a shortened version of the text?
<bot>: Good friend turned FWB now hates me because I slept with someone else. I feel horrible for hurting his feelings, but I thought our fling was done. How should I proceed?