His wife has become suspicious, and she has contacted me to ask me if I know why he's been acting differently recently. Should I tell her what I know or keep out of the whole thing?
A: Oh, blimey. None of this is your fault, but whatever you do (including nothing) is going to be nasty. So let's try, by a process of elimination, to work out your least worst course of action.
For all the sympathy you must feel for her, I don't see that you can possibly tell her what you know. For starters, you don't know enough; you don't know if your partner is having a fleeting mid-life fling or is seriously contemplating a second marriage. If you tell her anything at all, she'll quite understandably confront her husband with it; who in turn will ask you with some steel in his voice what the hell you think you're playing at. So that's out.
You could choose to do nothing: always tempting, and surprisingly often right. But not, I think, in this instance. She's already been in touch with you once and you must have done a bit of hasty dissembling. I doubt if she found you very convincing. She must be having a horrible time, so is almost certain to be on to you again. You can't go on lying indefinitely.
So you've got to talk to your deputy. Try to avoid any hint of confrontation or Edwardian disapproval. Tell him that how he spends his own time is entirely a matter for him and his family; you're making no judgments, taking no sides, and are profoundly uninterested in knowing any more about it all. But, through no wish of your own, you've now become involved; and you're not prepared to go on lying on his (or anyone else's) behalf.
If his wife calls again, which she almost certainly will, you intend to say as gently as possible that you believe her suspicions to be well-founded and that she must talk to her husband.
I've no more idea than you how this mess will get sorted, but I'm pretty sure that's what you've got to do. Good luck.
Jeremy Bullmore's responses to work dilemmas in MT are collected in his new book Another Bad Day at the Office? (Penguin, pounds 5.99)
Please address your problems to Jeremy Bullmore at: Management Today, 174 Hammersmith Road, London W6 7JP. Or e-mail: firstname.lastname@example.org Regrettably, no correspondence can be entered into.