Um...what do the huge flags flapping in the breeze, the glare from the rockets, and the view in the stadium during Nebraska football games have in common?
They're all red.
How many red flags do you need before you figure out D isn't likely to ever be forthright with you and always withholding a good deal of information?
No, that's not "standard practice" in healthy, functional relationships. It's not necessarily dishonest, though it is rather dysfunctional. If you're looking for a solid, functional relationship, I reckon you need to be looking elsewhere.
Enjoy your relationship with D as it stands or end it. I doubt it'll change much.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.