I forgave him for being late, but he still keeps being late nearly every day.

Forgiving a person may give them an opportunity to easily change their behavior. Yet it is possible that he may continue to do the very same thing that you forgave him for. I see the purpose of forgiveness to be much greater than changing another person's behavior. For me, forgiveness gives me an opportunity to put aside my anger, resentment, fears expectations of the other person so I can think clearly and communicate effectively. I can then create workable agreements in stead of blaming somebody else for my upset. If I want to be on time, I could be responsible for that by making arrangements so I will not be delayed even if he does turn up late. Not only would I be on time regardless of whether he was late. I would also be allowing him to be responsible for his own schedule.