OK, so a bit of background. Sorry, but this is going to be a bit complicated (and embarrassing in parts).
1) The 15M (Spanish Revolution) movement decided to March on Madrid, the country's capital. There were (I think) 7 main branches of the March, starting off from different corners of the country. Probably only a few dozen people in each branch started off, but they gathered extra marchers along the route, so that several thousand walked into Madrid from different directions all on the same day. Added to these were people who couldn't take time off from work to march, but bussed in for the big demonstration in Madrid on the weekend of 23/24 of July.
2) Due to several other commitments (including the need to look after my vegetable garden and work for my local city's chapter of 15M), I knew from the start that I wouldn't be able to stick with the March from beginning to end, but REALLY wanted to be on it for the beginning few days and for the last few, entering Madrid.
3) On the first phase of the march, I was wearing a badge with a polyamory design
(but with a black background), and a woman from my local city, someone I'd come to really like (and found attractive) said that she really liked it, asking me if I'd give it to her.
4) I said that she shouldn't wear it just because she liked the design, only if she was in harmony with the meaning
of it. So - of course - this led to my explaining polyamory to her... which led to a longer conversation on the subject.
5) She liked the THEORY of polyamory, but had a LDR [long distance relationship] with a jealous man. They were even contemplating marriage. And this isn't your usual LDR. She lived in Spain, where they'd lived together for 5 years, until he returned to his native Argentina. We're talking 2 continents here! He was trying to convince her to move there, and his parents were backing up his plea. She was planning to fly out for a visit... and see how it went from there.
6) We felt a great deal of affection for each other (at least, I did for her and she seemed to for me); we were spending hours together, walking along the road from town to town and talking about intimate (among other) things; and as I wrote earlier, I found her very attractive. Anyway, the subject of a possible sexual relationship between us came up.
7) I explained that polyamory doesn't include cheating, and that she'd have to deal honestly with her boyfriend and his jealousy if there were to be anything sexual between us. She promised to bring it up with him.
8) I'd already explained (right from the beginning) that I'd be dropping out of the March after a few days, to rejoin it later. By the time I actually did drop out, my vegetable garden had gone for 2 weeks (in a hot June) without watering. The morning I caught the train back to our city, she pleaded with me to stay with the March. I begged her not to make the parting any more difficult for me than it already was and she ended up accepting that I had to go back.
OK, another break and I come at this from another angle (introduce another player)...