I think moving on and forgiveness are similar or probably interwoven and regardless of the magnitude of your holding on and bitterness aka holding grudges, it still only means that you're stuck and no progress has been made for the betterment of yourself or your circumstance. Moving on isn't about you hating the person you're moving on from, it's about welcoming growth and the realization that your attention, care, dedication, and love should be directed at/to someone/something worthy of it. You shouldn't be bringing yourself back inform of pettiness or getting a revenge. No one needs such negativity in their lives. You don't need it.