I have been offended at least 10 times by my roommate for the same thing: coming in late, being noisy, and disrupting my sleep. Do you recommend that I forgive each of these 10 incidents one at a time or can I forgive all at once for all of these?
I think you can forgive all at once for all of these, but at the same time, as you forgive, you should ask for fairness or justice from your roommate. If the roommate had been unfair to you in, say, three entirely different ways, then you could forgive for each of these independent injustices.
For additional information, see Forgiveness Defined.