I wouldn't say all ENFP's struggle with forgiveness. I would actually say those with Fi are very likely to forgive. I'm an ENFP. ENFP's don't like tension. Every now and then you find an ENFP who has a thing for drama, but it's not that common.
Someone with Fe is MUCH more likely to hold a grudge than someone with Fi because Fe people have to expand with their feelings whereas those of us with Fi can just go sit in the corner of our bedroom and sort through our feelings, come to discover some moral or lesson and feel better. Fe peeps are much more interested in retribution.