Rather than doing that, why not tell your wonderful friend what a betrayal it is to his wife to whine behind her back because she want a to look after herself.
Ahem. On a site full of women whining about their husband for doing the same thing.
In all seriousness though OP. You are slightly jumping to conclusions (projecting?) about what is going on here.
If this was a friend of mine, I would be asking about what else is going on and why it worries him.
There could be a few things. Firstly, it might be a sign that she is feeling unhappy and unfulfilled in her marriage, that she’s finding it bored and stale and needs an outlet. If that’s the case he needs to talk to her to work out how they can make things better for her. He might be happy, but she might not be and no longer be satisfied sitting at home. If that’s the case he might need to buck his ideas up about how they live their life if he wants them to stay together.
Is she secretive about her phone or spending a lot of time on social media and messaging? Is he being included in this new hobby or does it involve her going to ‘gigs’ to which he is not invited? Does she get dolled up just when going to one place so it is a particular person she’s seeing? Is she mentioning a colleague or friend over frequently? If that’s the case it could be an affair.
He’s not wrong to question a big change in his partners behaviour and why it is happening. It could be a sign of general dissatisfaction with how life is at the moment that they need to address. I think most of us know are at least one women who gets fed up with a husband who wants to stay home in front of the TV every night in his tracksuit. Or it could be more sinister. I don’t blame him for wanting to find out why. But he needs to find that out off her rather than listening to guesswork.