Just answering the title of this thread without reading the OP.
It would seem an excuse would exclude any meaning to the concept of forgiveness.
In my understanding of spirituality: Forgiveness and blame are not mutually exclusive, so long as blame is not put on the person's essential character, but some chosen employment of their (false) character. Forgiveness is not a form of blindness (or blind faith). This sort of thinking is the source of a lot of religious cognitive dissonance.
By all means: forgive the person, but don't forgive an ongoing 'condition' that you aware of, which that person is attached to. If you see the condition no longer attaches to them, you can pragmatically order your relationship on that new assumption: but don't act so as to pretend to be ignorant of things you are aware of, and don't begrudge the person (forgive them) for whatever roles they have cast themselves as- inside your awareness.
Abstract note: Whenever you are aware of 'themselves' (relatedness to the world in general), you are dealing with a unholy entity: the only way to overcome is not to resist, but to forgive.
Edit: I wanted to add the following right away, but typeC had crashed---
If actions are in the past and not ongoing traits, on that basis you can discern a renewed affiliation;- if behavior is ongoing, that is a separable issue to the forgiveness of the actor. Discerning the state of behavior is tricky depending on the clear and direct nature in a person's culture of communication, and most people will be tinged with a danger that is paradoxically fueled by their standards of moral knowledge, which produce a level of deceit to engineer those moral appearances they've bought into, at the expense of keeping sight of the truth, and developing on that truth for a progressive purpose (by the liberty of the real choice, not a programmed judgement). Similarly murky dealings are unavoidable by a myriad of social programming that prevents open expression of intentionality, which is further complicated when people decide on being undecided, and therefore uncertain of their own intentions, and project responsibility onto a God of the world type-authority, where there locus of control is totally externalized, freeing themselves to live vicariously through the subjugation to the story of their life. What I just detailed is also a mild form of Solipsism.