btw
My friends just told me that it happens when you import dead Amell/Surana save with romancing Leliana
sweet maker, one true love here..This is sad and heartbreaking, wow. I will always romance him after that, just to help him get away from that ''one-sided'' feeling : /
"what she was like"...oh Leliana... 
Yeah, I totally feel you. There's no way I can not romance him now. I mean you can imagine that someday after the Inquisition he'll manage to find romance elsewhere if you don't, but I also have the terrible nagging feeling that he could also end up living the rest of his days alone. That thought saddens me like you wouldn't believe. He deserves a happily ever after. >_>
This does fuel my headcanon about my Inquisitor being the reincarnation/reconstitution of my Ultimate Sacrifice Warden's soul, though. Aww yisss. I'm going to conveniently disregard the existence of Trevelyan in my head. oops. 
Same here. I've seen most companions & advisors romance on youtube. Still like Cullen's best. I just like the sweet & gentle & deep one. (Okay, I really feel that Cullen's very deep). His story arc, the whole part of it, just feels warm on the inside.
Yeah, I think that it's easier to appreciate Cullen's romance when you've seen the struggles he's been through in the first two games and realize that what he wanted with Amell is the same sort of life he can see himself living with your Quizzy for the rest of his days now. Ever since Origins he's envisioned that sort of happily ever after - and it's finally within his reach. He's earned it! Precious cub needs some happy in his life. 