What are you going to tell your in-laws if they ask you straight out, if their son is having an affair?
Or even if they ask you what's the problem with you two for that matter?
There are degrees of lying, and you have to wonder when that sort of thing is enabling, and what precedent you are setting if you actually lie to cover up an affair.
M-47,W-40,No kids D-filed 5/27/2010 Piecing - 10/21/2010 -=Soon to be banned=-