I wouldn’t say it sounds horrible. Challenging not horrible. Mental illness is an explanation not an excuse. So you are allowed to be mad. If someone unintentionally hurts you then you are justified in still feeling hurt. We learn to live with a lot of regrets in life. To me this would be a big regret for him to live with. I don’t see how he could live with this regret and not be angry or resentful or even unfaithful. You sound like a good and loving couple, so it’s not easy to just say “break up.” But it feels like that’s what I want to say.