I get that you think his cheating is justified. But cheating on your partner is actually never good or justified in any way. If, as you say, you weren’t good enough for him, he shouldn’t have cheated, he should have spoken to you about how he feels and that he thinks you might not be the right person for him. He could talk about the things that would be bothering him, and those things could be improved, but the only way that would happen is when both people involved in the relationship talk about their problems. You, I think, didn’t have any problems, but if he felt that there was something wrong/missing in the relationship, he should have gone to you to talk about it and not go off with someone else