I can say to you that you have started to heal already. You already understand that guilt was trying to take over. I can guess that you had a one night stand due to anger and retaliation, as well as emotional emptiness and despair. Those seem like normal emotions to me.

If you said no, I think the one night man should have slowed down a bit (and I have heard that in some locations, only yes from you declares consent.) That said, I don’t imagine you need to be too considerate with him should he show up again.

For myself , when my relationship was on the rocks, and my long distance partner slept with another man, I did not find it so hard to get past it. And the last thing I would want was for her to feel awful and disgusting and especially shamed. Best wishes !