Decision!
I always hate looking at threads here where you don't see the conclusion so here goes.
I've thought hard about my boundaries and we have had two lengthy zoom conversations. As I pointed out to her, she does have some boundaries RE her exes - she wouldn't, for example, go for a weekend away with an ex. So now we are in agreement that we both have boundaries, it's about agreeing on those so we are both clear.
What initially upset me was that she initialy labeled one of my boundaries (no one on one intimate dinners with former sexual partners) immature and controlling - as did some respondents on here. I get it. I do trust her so it's not just about the possibility of sex which she has assured is totally off the table, it's an intimacy (nice restaurant, date like environment, alcohol, etc.).
I feel that as this is a long term friend - not someone she had a quick sexual encounter with - the dynamics are different. They had been friends for a long time before I came along - they had a brief sexual fling when she was in a delicate emotional state (she had lost her husband of 20+ years). She doesn't see any issue with having lunch or dinner with him, or with her ex husband (she was married twice). So we have a boundary incompatibility - neither of us is right, and as I have seen on this thread, different people have different boundaries in this area.
She also clarified why she hadn't told this person about me. He has been given a cancer diagnosis and she didn't want to tell him her good news - that she had met someone else. I get that. I asked her, and she agreed, to send him a short text before they meet saying something like "Looking forward to seeing you and telling you about a new guy I am dating" - or something like that.
So we agreed that texts, calls, zooms, coffee / lunch / breakfast with her exes is ok, as long as there is transparency (she tells me - well not everysingle thing but if there's a meal, for example). We have a bit of a stalemate RE dinner. I said to her, "let's say you both happened to be in Paris alone, at the same time, would you have dinner with him?" She said she would. We've had to agree to disagree on that - I wouldn't do that myself and I would prefer her not to - but as she said well is London ok, my hometown, or Barcelona or wherever? So I agreed that although it wasn't what I would do, and I would rather her not, that I wouldn't throw my toys out of the pram or sulk - she will have dinner with these two men in her life.
Where had a big disagreement was when her first husband visits her, which he does occasionally. She is totally fine with him staying over in her spare room, while she's sleeping naked (as she does) next door. I'm not and I wasn't prepared to give on that. So she agreed if that were to happen she would put him up in a hotel.
So in summary we agreed - texts phone calls zooms lunch dinner ok - overnight stays not OK. We both feel listened to and I feel a workable comrpromise is agreed.
I would be interested in hearing others' boundaries!