If I may smuggle in a general point about poly, I see it not so much as an evangelical mission for full disclosure but as an approach to flexibly facilitate different loves with different people. A starting point here is respecting that everyone has their own arrangements for honesty. Gotta respect people for being real about themselves and what they can handle in theory and in practice. (I have to say there were times in a past 10 year relationship when i struggled through the night dealing with my jealousy while my partner was with another and found myself thinking, 'waaaait a minute! I wanted to grow up and be a writer/astronaut/firefighter, not a less-jealous person...!?!?' )
Second, sometimes you just connect with someone and you gotta get it while you can, how its available, bar cheating for my own personal ethic. Correct, I have no way of checking a DADT beyond trust. I think I made a good call and if I was wrong, then he's cheated on me too and I'll be rightfully well-pissed. (But cheating can happen even in full-disclosure relationships, not so?)
So on to the practicalities of finding satisfying ways of relating to people who sparked some connection with me. We live in different countries. He lives with his partner but both travel frequently. He might be back and I might still be available then or I might not, same I guess for him. The main practical thing during the time we were together was keeping separate social circles who know them as a couple from me, which wasn't very difficult although it made him cautious to meet my friends. Which made me feel a leeetle like sneaking, which made me feel uncomfortable, which led me to post here looking for others' experience...