You know what dialogue shows just how GOOD the Adoribull relationship is from the main game (not counting Trespasser because literally every line they have in Trespasser is an Adoribull Is Great Party)?
It’s not Bull’s ridiculous jokes and/or flirting, nor Dorian’s gamely responses to them. It’s not the sexual innuendos or Dorian not so subtly obsessing over Bull’s muscles.
It’s these lines right here:
Iron Bull: Dorian, you’ve been to Minrathous, right?
Dorian: Of course. I’m not a plebian.
Iron Bull: You ever been to that place in the Vivazzi Plaza? With the big, cracked bell hanging off the roof?
Dorian: With the dancers, yes. You’re making me homesick.
Iron Bull: Must grind your gristle the “Elder One” is some crazy Vint asshole, huh?
Dorian: I’m not thrilled to discover we should take those old legends at face value.
Iron Bull: Guess he thinks the modern Imperium is a real letdown, too.
Dorian: Why wouldn’t he? Tevinter once covered all Thedas, its glory only matched by its depravity.
Dorian: It’d be like Koslun showing up and learning the Qunari didn’t conquer the world after all.
Iron Bull: Hmm, yes. Priesthood’s been trying to explain that one for centuries.
The reason these exchanges are what I see to be the best proof of why they work as a couple is because it shows that both of these men look to each other for familiarity, with both being strangers in the South bonding over being from the North.
The first set of lines involve Bull and Dorian sharing memories from a place that Dorian considers home, and one that is closer to Bull’s home than, say, Ferelden or Orlais, that he’s reminiscing over.
The second set of lines show that Dorian knows more about Qunari culture than anyone else in the Inquisition apart from Bull, and has either shown enough interest to read about it or is aware of a decent amount about the Qun, as a citizen of Tevinter, especially one from Qarinus, which was victim to many Qunari raids.
Now this might just be me as an immigrant reading into this, but Dorian and Bull’s dialogues remind me of myself, as a person of colour and immigrant, talking to other POC and immigrants, especially those with a culture very close to my own, if not outright the same. We bond over things like temperature, food, homeland, and talk to each other about similar cultures, or even the same ones.
This isn’t even mentioning the fact that they’re remarkably similar for coming from warring countries, which Bull brings up twice:
Iron Bull: Think I know what your problem is, Dorian.
Dorian: I have only the one?
Iron Bull: You see a man who’s burned out, who left his people and entire life behind… and for what?
Dorian: You’re not suggesting we’re similar.
Iron Bull: How’s that mirror treating you? Pretty picture, isn’t it?
Iron Bull: Wait, wait, I’ll flex a little for you. Make it easier.
Iron Bull: You doing all right, Dorian? I know family stuff can be rough.
Dorian: What would you know about it? True Qunari don’t have families.
(If Iron Bull is Tal-Vashoth)
Iron Bull: Finding out you don’t fit in with the people who raised you?
Iron Bull: Having to walk away from everything you grew up with, knowing you’ve disappointed the ones who loved you?
Iron Bull: I might know a bit. Takes a tough man to do it, too. So good on you, you big old fop.
Dorian and Bull UNDERSTAND EACH OTHER in ways that few other Dragon Age characters do, both from a cultural / background perspective, and in terms of their personalities and character.
Add that to the fact that they’re very much sexually compatible as well as remarkably sweet even before Trespasser:
Iron Bull: Dorian’s a sweet guy. He’s gentle, and he cares under all that bluster. I’m hoping we’re good for each other.
Iron Bull: Plus, I’ve never done it with a mage before. One time, he got so excited he set the curtains on fire! (Laughs.)
Cassandra: So, Bull, about Dorian…
Iron Bull: Yes, it’s true.
Dorian: By all means let us discuss this together.
Cassandra: If… you’re both pleased…
Dorian: I’m happy, he’s happy, everyone’s happy.
Iron Bull: Awww, you’re happy.
Dorian: I’ve decided to stay with the Inquisition. For now.
Inquisitor: Would that have anything to do with Iron Bull?
Dorian: It might. You know how it is.
And you have a relationship that is a genuinely good one, built on chemistry (both in terms of sexuality and personality) and understanding (both intellectually and emotionally).
They’re both intelligent, driven, damaged, strong men of the North who remind each other of home, who are used to lies and masks but show genuine softness to each other, and know and understand each other better and more than any other character in Inquisition.
Which is why Adoribull is such a good Dragon Age relationship.