Thanks, good advice/food for thought from all three of you:
Ray, yes I've heard before that ex's tend to be a loaded situation but I think not particularly in this case. She was more a lover/"fuck buddy" than "partner" which was why I chose her now ie she wouldn't be felt as a threat to our primary relationship. What am I looking for? Well sex is a big part of it but hopefully in the context of a meaningful friendship, though I wouldn't say romance (whatever the difference is...)
nycindie, good to be reminded that being heard is the most important thing and thanks for saying I'm doing the right thing. That really reassured me! And the advice re. going at the slower one's pace.
redpepper again thanks, I'll let her know about the site and possibility of support. I don't think she would join here but you never know.
My date went ahead nicely and "innocently" on Sunday and had a really good intimate talk with my girlfriend afterwards and again last night. It's very much up in the air where we go from here, I feel uneasy she might think that's the end of it (being poly) but it's up to me to have the courage to keep talking openly about my hopes and aspirations.
I really appreciate your thoughtful responses, Nic