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.
Gralson: my husband. Auto: my girlfriend.
Zoffee: Auto's husband. Cue: Zoffee's boyfriend. Bookie: Cue's wife.
"Love is not breathlessness, it is not excitement, it is not the promulgation of promises of eternal passion. That is just being "in love" which any of us can convince ourselves we are. Love itself is what is left over when being in love has burned away, and this is both an art and a fortunate accident. " -- Louis de Bernières