Polyamory is quite often used an as excuse for cheating. The thing is, it's quite east to deflect that once you know a few methods.
First, for me, before anything sexual happens, I need to meet the other partners. If the other person needs to "go slow" for whatever reason, then I will go slow too - if this person is that good, then they are worth waiting for.
So, for example, in this case, once it was obvious that the sparks were there, if he was saying "it has to wait until after our trip", then my response would be, "ok, good, give me a call after your trip, once you have told her, so that we can do a quick face-to-face meeting with her."
I don't do DADT arrangements for the reason that it's far too easy to lie or misinterpret. I know far too many folks who have promised that their partner was perfectly ok with it only to find out later than the person had no clue.
From what you have written it sounds like you have a good, firm grasp on what you want and what you don't want. It should put you in a great position to negotiate the poly minefields that can be out there.
Please check out The Birdcage - an open, friendly Polyamory forum for all parts of New York State
"Listen, or your tongue will make you deaf." - Native American Proverb