Any way to ease into having a cheating spouse?

Friend of mine basically told me he saw a woman leave the house and his wife was naked 3 seconds later when he went inside. She gave no explanation. But he's somehow not come to the conclusion she's cheating on him.

I tried just saying that's what it sounded like and he wouldn't even consider it, even though he couldn't think of any other explanation. But if she's not being careful anymore then he's bound to walk in on it happening soon, and there's no way to not see it at that point.

I know there's not a way to make it less painful, but is there any way to get him to start realizing and dealing with it now instead of being totally blindsided later? Is there any way to push the idea slowly? He won't listen to it flat out.
Any way to ease into having a cheating spouse?
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