Even while we kill and punish we must try to feel about the enemy as we feel about ourselves—to wish that he were not bad, to hope that he may, in this world or another, be cured: in fact, to wish his good. That is what is meant in the Bible by loving him: wishing his good, not feeling fond of him nor saying he is nice when he is not.
From Mere Christianity
Like forgiveness, love isn’t initially an emotional act, but an act of the will. When at last you obey God’s clear command to forgive the unforgivable, or love the unlovable, He will pour out His grace through you in a torrent of love, second only to the love He felt for the false witnesses, the Roman thugs, and the world of sinners like you and me, all of whom conspired to nail Him to that cursed cross.
Loving your enemy won’t come easily, but it’s what Christ-followers do.