The answer always comes out the same...
Actions over time.
When I deal with the past as it comes up in my thoughts from time to time, I need deal with it as it comes up...in the moment. Forgive again if that is what I need do but I don't forget because I tend to remember the hurt and don't want it again. I need do the same for my own actions of the past as well as the actions of others of the past.
My own actions over time (proper actions) help me heal.
The actions of others over time, help me forget and heal.
From what you posted... His actions of today may be what is fighting your wanting to forgive his yesterdays. When he grows more in his recovery and starts to realize where he needs to make amends and own up to his past... his actions will support your wanting to forgive his past.