I had an affair a year ago and the guilt keeps me up at night.
Is this the guilt that keeps you up at night?
Yeah, I'm sleepless because of the guilt I've been suffering
I am sorry you have these feelings and a difficult past. It is good to forgive yourself for your past mistakes.
I'm not going to forgive myself until she forgives me.
You should talk to your former partner in order to get rid of your guilt. If it was your fault for whatever happened between you, you need to apologize. If you want closure, you should discuss openly  about your guilt.