I'm not sure anyone can really help you out on this one - its a question which taxes or has taxed many of us here but for every person there is likely a different answer.
The ability/propensity to forgive is something I think which is an integral part of an individual's psyche and not a quality which is easy to define or learn.
Personally,I've found the "its a gift you give yourself" angle useful. This internal perspective has helped me deal with it.
