ask him about it, tell him you're not judging him, but that it's not something you can tolerate in the marriage.
see where it goes from there. encourage honesty - you have to make doing the right thing (opening up & sharing his heart with you) the easy thing to do.
what would you do if you moved into a brand new home & found a few bugs? not a huge deal, right - though very disappointing. exterminate.
let it go & you could end up with a pretty big problem down the road.
are you prepared for the possibility that there may be a problem already? that he might have a hard time letting it go?
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