When my (ex) h and I first tried poly, he made the same deal with me. If I ever became uncomfortable with him loving another woman, he'd put my feelings and needs first, and stop trying to be poly. Well, I was OK with him dating and falling head over heels in love with this other woman, H, for a while... I tried to give them space to date, to have sex, even though originally we were (stupidly) looking for a "unicorn" to share, and despite early indications she was interested in both of us, turned out she wasn't.
But after 4 months I just couldn't deal with their NRE anymore. It was so over the top, and after being with just him for 20 years, I had no idea how to handle him being all twitterpated over someone new. (Even though I feel I am more wired for poly than he is, and got crushes on friends constantly.)
So per our agreement, I vetoed the relationship. This backfired however, and they remained loving friends, even though the sex stopped. Eventually it bred bitterness and was a factor in our marriage dissolving.
(I'm doing much better since he and I broke up in 2008, don't worry. I was ready to move on too, for various reasons unrelated to poly.)
Anyway! Be forewarned that you really can't close the barn door once the horse is out.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
Mags (poly, F, 61) loving miss pixi (poly, F, 39) since January 2009, living together since 2013
"Master," (mono, 34), miss pixi's Dom for 3 years