@mimimimimimi,
From evolutionary biology point of view: there is a reason why women tend to forgive cheating faster than men. If has things to do with resource access etc. If you are interesting in knowing more, I suggest do some research to understand why men might feel hurt about this and take is seriously.
about you:
every person is simply different. Some may take it easier, some not. I think his reaction was pretty legitimate - he did not create drama, not shouting, no bad emotions, told you he lost his trust and therefore he is leaving you. I think you did one very nice thing: were honest with him.
From this point of view, no one did a mistake and life is going on. You might or might not try to reconnect with him, no one can tell you what to do or predict reaction.
Also, PUNKEY - cheating is a bad thing for sure, but we do not know circumstances behind it, so I would not be judgmental.