Here are all the results with descriptions
You should forgive him, because clearly this guy is a) into you, b) clearly has a good personality, c) is very much sorry for what he did, and d) clearly values and appreciates you and had a momentary lapse in judgement. He's learned his lesson, and deserves to be forgiven. But note, only once. If it happens again, it's over.
Forgive, But Set A Trial Period
So this was a thing, but it wasn't the worst. What he did wasn't the end of your relationship, it wasn't that grave. But it was serious and as such, it means you are now unsure of what you can expect from him. Just what is he capable of? What happened caught you off guard. So... put him on a trial period without letting him know. Forgive him, carry on, but pay careful attention to things he says, and what he does. See if this is the person you fell for in the first place.
Forgive, But Be Super Wary
It's okay to forgive, but feel the need to shelter yourself for the sake of... just wanting to be careful. Protecting yourself is nothing to be ashamed about. That being said, there's a limit. There's only so much you can mistrust someone before they begin resenting you. So, try this: forgive, and give them a chance to prove it was a one-time thing. Be suspicious, be wary, but don't remind them constantly. If you feel uneasy, gather SOLID evidence before 'putting him on trial.'
What he did was beyond anything that anyone should ever do to their partner. But it happened, it was real. It happened to you. And although it takes two to tango, it doesn't give him the right to crush your heart and spirit. If things were that bad, he should have just walked away. So, it's best that you don't forgive this time. Because this isn't behavior that just up and changes because you deem it so. In fact, it's been going on for a while. Thinking back, there were plenty of red flags.