If your husband was off for a large part of the week and in another city and celebrating out until late drinking alone with another woman and you're at home looking after the kids, had a busy busy day making sure they're all fixed up, done school, got home, given them dinner, done loads of washing etc and then you find out your partner is living it up in a hotel bar with someone else it would probably make me feel a bit insecure.
I'd want to know why a large part of his time and success and happiness was being shared with someone else.
I'd expect him at 10pm to cut it short, come home, phone me and talk to me for at least 30 mins and reconnect.
No wonder his wife feels insecure. I'd give my husband shit too if he was always celebrating the high times, good times, out with someone else, even if it was a man - it would get annoying.
There comes a time in everyone's life when you have to grow up and put family first.
There's nothing wrong with drinking with a man alone but it's everything else.
Perhaps she's a stay at home Mum? Perhaps he really doesn't spent enough time with her to make her feel valued - and if you're a really kind person - you'd reflect that question back to him to help him work out if he is doing enough and help that marriage and take the onus off you and it being all about you doing something wrong and help that woman feel better about herself.
People may say oh it's not your problem - but maybe it is. Maybe he doesn't do enough at home. Why else would she be worried. No smoke without fire - usually.