I read about your situation recently but didn't have the ability to reply then - I've just moved and only just got wifi back - anyway, I know we don't always see eye to eye, but I do want to express my condolences sincerely and I hope the situation improves with time.
With regards to the question at hand - I'd worry about how this may affect your own feelings, could it lead to resentment? Perhaps it would help to trivialise it a little which may be what you're aiming for (even though it's far from trivial in reality), but if you were to go down that route I'd maybe suggest it'd be worth setting a time limit, after which you can draw a line under the whole situation. It isn't fair on either of you if this becomes a long term issue so forgiveness and ultimately forgetting about it is important but that does take time and perhaps your idea might help whilst you're working your way there.
I can't see it'd be a great idea to bring the third party into it though, even if they weren't to know. Then you make the issue about the other person when in fact they don't matter - what's important is focusing on reconciling with your partner!