For me, forgiveness is a process driven by an 'aspiration' to forgive if I choose to do so when I choose to - for both selfish and altruistic reasons. I sometimes feel it is easier to forgive major things than the smaller everyday betrayals as it can be a grand act that puts you on the high moral ground, or used as a weapon as Joan suggests.
I think there are several levels of forgiveness - one needs the perpetrator to accept they have done wrong (rare, I fear), show remorse by actions as well as words and make reparation of some kind. Forgiving unconditionally is a much higher level which only very special people achieve. I stay at the bottom, wishing I could forgive but often don't really, long term & don't see why I should put in the hard work when the perpetrator does nothing.
My solution now is to say that if you can't get rid of a rotten tree then grow another so that it overshadows it and makes it increasingly less important in your life. The best thing to be done with anything bad is to redeem it through learning and to turn the bad into something good for yourself & others.
A few years ago I was in a research group with an amazing woman, Marian Partington, whose sister Lucy was one of Fred West's victims. She introduced me to the Forgiveness Project. Do have a look at their website
http://theforgivenessproject.com and read her long journey of discovering what forgivenss really means, beginning with her feelings of intense rage. She used the term 'lining yourself up for forgiveness'
