Yeah I know. Mind you I don't understand it but if we got into my views on love it would be extremely longwinded and off-topic so I'll just say that I hope future!Dorian has found the wisdom that current let-me-bait-you-with-escape-routes-to-see-if-you-leave Dorian presumably hasn't.
Dorian is a lot like Jack when it comes to the whole romance department. He's so afraid that everything is going to turn sour or come crashing down at any moment so he wants to keep some kind of failsafe option around just in case.
There's also the feeling that he's not entirely comfortable with being the Inquisitor's boyfriend. He genuinely loves Adaar/Cadash/Lavellan/Trevelyan, but he's not big on the title or what people will assume about him because of it. Which is pretty interesting, since Dorian is the first Bioware character that I can think of who
isn't happy when we use our "Because I'm the Protagonist" power to help him solve a personal issue.
This is just me, but if/when Dorian goes back to Tevinter I'd be willing to bet that it's going to be pretty hard for a romanced Inquisitor to not have the advisors give him a helpful little "nudge" every now and then. Or this:
Dorian: Varric, I know he sent you.
Varric: You know Sparkler, not everything revolves around the Inquisition.
Dorian: You've set up shop at the tavern near the Arcanist's Hall, why would you be here other than him asking you?
Varric: I'm on sabbatical, Sparkler. They haven't rebuilt my tavern back in Kirkwall, and after what we just went through I decided that taking some time to visit family was a good idea. The senate's in session so Minrathous it was.
Dorian: So the three casks of Ferelden beer and my favorite chair from Skyhold showing up at Maevrais' town house at the same time as you did was just a coincidence?
Varric: No, the boss wanted to send a little care package for you. He understands that you need a little space for...whatever it is you're doing.
Dorian: (sighs) Please tell me that you didn't have to drug him this time.