axl, it sounds to me like you and your h have discussed all this opening of your marriage fullly before taking the plunge. If you feel fine while he is out with K, dont go looking for trouble. I'd say most people would feel some jealousy, feel a little insecure, when their partner is out for their very first poly date, but then again, Ive talked to people who say they don't have a jealous bone in their body.
The only concern I have is where you said you suspect your h and K have already had sex, yet he won't admit it. That needs to be cleared up. A little white lie here and there could lead to trouble. My gf and I are always completely honest and open about our activities and feelings for other partners, even if it hurts. It makes for more trust and good times in the long run.
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
also loving Punk (42, M) since Oct 2015 (he has recently downgraded us to friends)
"Master," (mono, 34), miss pixi's Dom for 2 years