And yes, of course you tell them the truth. Why LIE to cover up HIS affair?
And when your H complains because you "exposed" his affair, and he WILL complain you tell him the same thing :
I refuse to lie to our friends and family to cover up YOUR infidelity.
Note I didn't say "telling"... which is what children do... this is an affair and you expose it. You aren't tattling on a child here. This is a man and he has responsabilities and he's HIDING behind a lie to escape his responsabilities...
DO NOT ENABLE infidelity by covering it up for your cheating spouse.