Truth without love can be harsh, judgmental, and dogmatic.
Love without truth is blind sentimentality.
But truth in love is compassionate concern.
If you love your wife, you'll talk to her family merely because they should know the adulterous path your wife has chosen and that this guy that your wife intends to bring around sometime in the future is a viper. Affairs are destructive. Whether you save your marriage or not, your wife is in a soul crushing and destroying relationship right now that someone needs to save her from. Who better than her loving husband??? If her parents are God fearing Christians they just might try to save her and help you in the process. They may not. Either way...YOU were honest with them.
All I'm saying is don't lie to protect her. If asked...speak the truth.
Consider this ~~~~> It's also not SELF-RESPECTFUL to lie to your in-laws.
Don't lose yourself in these circumstances trying to look out for your wife or think that if you protect her she's more likely to come back to you. You are NOT a liar....so don't lie for her. Lying is what way wards do and it doesn't help your situation.
The internet is 90% complaining and entitlement and I hate it because I deserve better!