I told her yesterday (!!)
I tried to be sensitive and careful. As I guessed, she is not and "will never" be too much into polyamory... At least, she didnīt dump me (which was a real possibility), understands that I have desires, says she is thankful for having been frank... Her attitude towards me is serene and understanding, but she is kind of "itīs that polyamory modern thing or me" , "donīt harbor futile expectations about this"...
So itīs kind of a crossroad.
If things stay as they are now, I will probably try again later: I like your suggestions of participating in a group together,etc. I donīt really think sheīs going to join a meetup, etc. but at least she is willing to read. I will let her see some stuff I had prepared (a collage with some ideas from this forum and other polyamory sources).
Thanks a lot for your reply!
lots of love and peace