To all of those who commented previously, thanks. Reading it again now, 1 month down the line is therapeutic.
By way of an update, things have become worse. Things became bad at home, as she had another secret rendevouz with this guy ,and as she had become so secretive again my susicions became aroused, and when ultimately challenged, she admited she'd seen him - although denied any intimacy (which I don't know whether to believe or not).
Since then, things became so bad, that she moved out, moved in with friend and has now moved all her stuff out. At first saying she needs space, but then saying it's over. We are still in touch, and I know she sees this guy. The situation is not good for me, and I am going to get help dealing with it.
She is still however saying that she wants an open relationship, with me as the main partner, that she sees me as a her life partner,just not now. This has made me feel like a toy she puts down when she's found a new toy, and will pick me up when she get's bored of him. I've told her this. She accuses me of being possessive, a typical male, that I'm treating her like a trophy.
Finally, I have put a proposal to her. That if she absolutely has to have him in her life right now, I will agree - but not an open checkbook - it would have to be on terms I would be comfortable. I've suggested 1 date day/night per month with him. to start with, to be reviewed.
I've also said she has to stop seeing him for now, if there is any chance of us having the future she envisages, as this is not good for me. It would be a situation like me, joining them in an open relationship, rather than him being added on as an extra, an occasional lover.
Finally, I don't want the development of a parallel situation, and as such told her I wouldn't be comfortable with constant contact, daily texts emails etc. She told me she just won't communicate with him while I'm there, but I don't think it matters whether I'm there or not. This thing would need to have clear boundaries for me.
Am I being unreasonable? Opinions and judgements all welcome!
I've re-read some earlier posts, and I agree with those who said situations like this are definitely not the right time to add another person, that you focus first on the core relationship. But I don't think she is prepared to wait for him at the moment. The fact that she ended us, in order to get the space she needed (in my opinion to see him) shows that it is almost like a non negotiable term of having her back in my life. I am on the edge of walking away from all this, but before I do, want to get as much feedback as possible from people with similar experiences. And I will get professional help to deal with all this, and deal with the life changing decision I am faced with. Just to add we had an initial assessment for couple therapy last week, so might have a proper session in the diary soon. Thanks for reading.