"You can't forgive without loving. And I don't mean sentimentality. I don't mean mush. I mean having enough courage to stand up and say, 'I forgive. I'm finished with it." - Maya Angelou
This quote resonated with me as I also believe that in order to forgive, you need to first love yourself.
This means first looking within and identifying if there is any way you might have contributed to the situation and if so, then moving into compassion for yourself and into an intention to learn about your role. Once you have the courage to do this, you'll find it's a lot easier to then move into compassion for your partner.
If you're clear that this isn't about you at all and this is something that was done to you, then you might want to consider how holding onto the anger and resentment and hurt is helpful for you. It isn't right? So here you are struggling with these difficult feelings yet you're not willing to let go of them by moving into forgiveness. One reason partners do this because they believe that "If I forgive my partner he/she will think they didn't do anything wrong". Another is the belief that if I 'punish' my partner, they'll never do this again.
Forgiveness isn't about the other person. It's about you. My experience is that when you focus on your partner and what they did or didn't do then you're not taking very good care of yourself. Instead of perpetuating your difficult feelings, you can choose to forgive so that you can let go of these feelings and you feel better. Forgiveness is really about freeing yourself up to move on rather than releasing your partner from taking responsibility for their unloving behavior. That's not something you can or probably want to do.
My experience is that the more you value yourself the more courageous you'll be to forgive. And when you've set yourself free from those difficult feelings, you'll know what it looks like to take loving care of yourself in your relationship. You'll know how best to address what happened in a more loving way that doesn't include holding onto those painful feelings which are really only hurting yourself.