Well, I think part of the underlying thing with Dorian and Klaus (and I've gotten some flack for this) is "they can't". It's pretty obvious that Dorian only wants what he can't have, and the reason Dorian has stuck with Klaus for so long is because he's the ultimate "can't have". If Klaus actually gave in, Klaus's iron pride will have been compromised, and what makes him so appealing to Dorian would be gone. Dorian would eventually lose interest, like he did with Caesar. So the outcome would not be happy, and I find it really hard to ship relationships that I can't see working out to a reasonably happy ending for everyone involved.

And, yes, it really depends if the couple is the destination or the journey. I've been rereading my favorite manga romance ever--Galboy--and Akira and her boyfriend marry very early in the series 40+ volume run, and the rest of the series is about them experiencing the ups and downs of being in love and living together.