I wouldn’t be so hard of yourself. people don’t just break up for one reason. He might have had an idea he was going to break up before and this just tipped him over. You said it was instantaneous, maybe he was ready. I’d never just assume things were going as great as you thought they were with a Libra, as Libras charm automatically. Besides, you should be able to relax with someone.
Are you still communicating with him now? I can’t tell from your question. Your focus should never be on the bad, always the good. Ideally you want to forget this happened, and try to meet him and get back to how things used to be. I know he said the problem is communication, but it isn’t (wow Libra men are like women, seriously). Never ever apologise or talk about what happened or the pot. Switch the entire focus, your aim should be to have a good time. If he brings it up, try to say “was it really that bad?” And laugh if the situation allows it. Try to make him wonder if it was that bad, you want him to forget.