Why does it always start with a card, and a recently separated woman in her forties.
I wonder how many mumsnetters had this.
He's probably a bit giddy with this possible new found friendship, you will notice a spring in his step, but mention it to him and he will become defensive and start slating her.
As for her atempt to encourage mild flirtations to keep the punters onboard, if she had any sense, if those punters are married it's a sure fire way to decrease the numbers, once a wife finds out there's a predatory single middle aged woman moaning about her breakup.
It's not profesional, she should respect people's home and family life, leave off the kisses and be inclusive with the group.
There's not much you can do though, even if you stopped his gym visits, he would hate you for it, and if he continues, you will end up hating him, it's embarrasing having a 45 year old love struck idiot in the home, your daughter has cottoned on.
Good luck, barring an accident this one is going to play out...