I dun really think it's a case of having a bigger heart or needing vengence per se. U can indulge in bitterness or feelings of anger, disappointment, etc for a while but I believe that eventually u will move on and that's it. No need for the other party to seek forgiveness, in fact dun even expect that. Just let it slide off ur back like water on a duck's back. Easier said than done? I think to the other party who hurt u to the point beyond forgiveness, it is probably more disturbing that u feel "nothing" instead of "anger or hate. The opposite of love isn't hate... it's just indifference. The whys, hows, whats wun even matter but it's human nature to want the answers anyway.
Actually, the easy part is to forgive, but it's so much harder to forget. Sometimes u can forgive and are ready to move on, but to re-establish the trust that was broken is many times harder, sometimes impossible.