It is easier to forgive an enemy than to forgive a friend.

An enemy was never trusted, so the damage they do costs you only the injury itself. A friend borrowed something first, and getting past what they did means also facing your own judgement in having let them close. That second bill is why old friendships end over things smaller than what enemies do without consequence.

If you are still angry at someone who was close, separate the hurt from the embarrassment of having trusted them. The first can heal. The second is about you, and it eases once you stop treating your own trust as the error.