When a couple argue, one will forgive one, else they will break up.
Sometime they are forced to forgive, else they have to break up.
You know it, if you don't forgive him/her, the one who actually did wrong will blame and point back to you that you are small gas and not tolerate enough.. mm ok.
Sometime you even have to act that you have forgot about the incident.
Forgive someone is easy, but to forget what he did is hard.