Would you forgive this honestly? Please be honest.

Do you think he is wrong for feeling outrage? No, his feelings are valid.

Do you think that he should just forgive it because it happened ten years ago?
Yes.

Do you think his request for her to gain forgiveness is too much?
I think his request sounds more vengeful than it does actually act as an action to repair what they have. If it was a decade ago and over I suspect confrontation could unnecessarily damage the relationship the other guy and his partner. If he doesn't trust the other guy, then maybe that friend should no longer be in their lives if they are to continue as a couple.

Can the other guy possibly think he wasn't in a affair? That affairs only happen when you have sex, and that he was always just a friend all along? Wouldn't that be the basis of a awesome lawsuit against this crazy guy demanding a confrontation for a nothing event from a decade ago.

For all I know I've had ten to none near miss relationships that was emotionally felt by women, that I never knew about, because I wasn't aware I was in a relationship. If I don't register it, how am I supposed to know it is happening.

Maybe some of the guys here who think they are isolated lonely losers are serial romeos, who don't realize they've had a score of emotional affairs.

Your age is 36 - 40 right .
If that was 10 years ago would your friend be about 26 - 30 when that happened .
Depending then on how long they were in the relationship before the person cheated , take off that age again . Do the maths ?
Then if your friend got cheated on at that age and if the person they cheated on was around that age.
Like from 20 - 25 is still fairly young at that age .
There's still maturing at that age so my answer would be would you forgive them .
Yes .
When I was talking to an 88 year old man on day and he asked me how I was ? I told I was demented . I was 37 then .
Do you know what the answer he said to me was ? Your only a young fella . There's f**k all wrong with you .
He changed my whole idea about forgiveness.
He was 88 and he was after living life .
And to top it off .
He was very happy

Your friend seems to have the emotional maturity of a 7yo. He needs to get a grip on reality and understand that nobody is perfect and we all make mistakes.

Let it go, it was a long time ago, and why start trouble?

10 years ago, 5, 3, 2, its irrelevent how long ago. Its valid. I would be hurt and feel insecure. Trusting is hard enough. I have been on both sides.

I would walk away. From her and your friend. I have seen that movie before, and it never ends good in my experience.

Not at all.