I don't have many links to infidelity fics - as I said I avoid them generally. Out of 606 fics tagged on delicious, I have only saved 3, tagged "adultery/betrayal". The Blue Door by snegurochka_ lee seems to be the classic - it's the one that blows everybody away, even if they NEVER read snupin or infidelity fics. It's simply brilliant & unspeakably moving. And it's almost as interesting to read the comments after the story has been completed - readers appear to be in a state of near-shock. I know I was. There's also busaikko's As Simple as That. Heart-rending/heart-breaking, beautiful & so moving. And then the Epilogue, which is essential reading, here. And busaikko's The Bad Year that may not be what you want as,as it's part of a series & really should be read after "The Waltz Continues", & "The Burning House". Still the quality of busaikko's work is extraordinary, & this story never fails to make me sob. Both "The Bad Year" & "The Blue Door" have been tagged with my "ANGST WARNING" in delicious - & both have descriptions starting with "I hate this, I hate this - I can't read it" which gives a fair idea of how bloody moving they were. And I DID read them, & save them too.
Intellectually, I agree that's there's no harm if the adultery is unknown (& finished). However, emotionally, I think there is always some level of awareness (even if sub-conscious) & that could do damage to the relationship. I do hope you read some of the fics I mentioned - they are classics of their kind, & extraordinarily good. I really meant it when I said I didn't like infidelity fics - when I tag your fic it will be one of 4 fics (out of 607) of that genre saved!