With regular people there is something to forgiveness but if you are dealing with a sociopath, which you usually are if they are liars/cheaters/abusers then forgiveness ends up being a way to enable them in their twisted minds that its okay to harm others and not have to face the consequences of it. Their karma/judgment/whatever is their business but for the abused/betrayed partner it means it will be a cycle that never stops. They can forgive another person in their heart but they'd better get out of that situation for their own safety and survival.