I personally believe that you have every right to talk to his wife and be supportive to her. By the sounds of it, it's possible she's in a controlling relationship, in which case she's going to need help and support from people who care about her in order to fix that.
I've never been very good at keeping my nose out of other people's business. I don't tell people what to do, but I make sure they know they have options.
Sadly, it's not uncommon for people to be hypocritically non-monogamous. They want to have multiple partners, but they don't want to extend the same opportunity to those partners. So not cool.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker