Would you tell your friend that his/her spouse is having an affair?

Unless I walked in on them having sex or something then how would I know there was an affair happening? Whatever I saw, I'd take a picture of it and let my friend draw his/her own conclusions about what was going on. "I ate at Dino's last night and saw your spouse there. Here's a picture." 

I wouldn't say say anything about any suspicious I might have. First, it's none of my business and second, that would be awkward for my friend. If he/she wants to talk about the spouse's behavior, let him/her bring it up. I'm not going to. 

If you have it on good information........

YES. 

This question often comes up. On one hand, its none of your business and you could even create problems for yourself by interfering. On the other, it might be not only appropriate,but much needed for you to inform your friend. What if he/she becomes infected with AIDS because their partner slept with someone who transmitted it to them? At least, they should go get tested !  In any case, wouldn't your friend want to know? I would tell them. But first, I'd want to make damn sure I was right!!!

Maybe.         

Yes.........................

Yes, because I'd want a friend to tell me in the same situation.