To me, forgiveness is realizing that as "black-and-white" as I saw my wife's transgression against me as being, I have my own shortcomings . . . they are just in OTHER areas. That doesn't make me any better . . . or any worse.
It's the whole "all have sinned and fallen short of the glory of God" thing.
So to me, forgiveness in my marriage means walking humbly in constant awareness that Starsky ain't all that either.
So that's part of it.
The other part is this TOTALLY humbling realization of, "If GOD HIMSELF -- THE CREATOR OF THE UNIVERSE -- didn't give up on my marriage . . . who the frick was *I* to? I saw things -- and still do! -- that show He is fighting for my family, so I just kinda figure "Who am I to do any less?"
But to answer your question, I do think it's a DECISION . . . or even an OBEDIENCE (to God) thing. The feelings will then follow, in time -- at least they did for me.