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Thanks for your answers. I'll think about them all.
Quinlad Tricky is a good description. It is so very difficult.
Vic, you say you're not sure why I am embarrassed at her paying for lunch. Would you be happy if a friend continually footed the bill? I'm sure she is generous, but I am far from poor, and I do find it patronising - and frankly a little humiliating. Incidentally, we meet at very good restaurants, so the bills amount to a great deal more than your estimate.
Being invited to someone's home for lunch is a completely different thing, and of course I wouldn't expect to pay, but this is not an invitation - it's a group of people who agree to meet twice a year for lunch.
Coco, I have done that - but I'd rather just pay the bill. (By the way, where have you been? It's good to see you back. Are you ok?).
Octavius, yes, I'm thinking that way. The last time we met, I had the usual argument, and in the end I suggested that if she insisted on paying this time, then I would pay the next time, and perhaps after that we should take it in turns to pay for lunch. The response from one of them was ""You must be joking!", so as you can see it's really difficult, and I can't help thinking that, sad as it is, it could well be Christmas cards, and perhaps the odd email only in future.