This is great advice, really good post!
If you do truly forget a transgression though, you would have a problem dealing with repeat patterns of behaviour. You have to be able to recognise a pattern, so that you can ask yourself "Is this aspect of their personality something I can just accept as part of the relationship, is it something I should try to change about them or is it a deal breaker?". In some cases you may have to forgive a close friend or partner prospectively, impulsively making transgressions may be a fundamental part of who they are. You may have to cut a relationship off for repeat transgressions if you cannot accept it is part of who they are, in which case you need to remember the transgressions that you previously forgave. For example, if you imagine being in a friendship with someone with ADHD, or even anti-social personality traits. Since they are intransient, going through a cycle of getting upset, then forgiving and forgetting is going to be the most emotionally draining of the options available.