Though I do wonder why it took Fenris three years to ask for Hawke's forgiveness after sleeping with her, then leaving, I like the way the romances in DAII progessed over time. In Origins I met Alistair, survived Ostagar with him, we ran around, I gave him his mother's necklace, saved some people, then got laid. While that is not the unbelievable part, what gets me is that he says he loves me. While I believe he means it in the moment, and I can suspend my disbelief, I can't help but think that if someone did that to me in real life I would definitely pause.
But in DAII, with Fenris specifically: He almost got me killed by luring me into a trap meant for him, then asks for my help. I willingly agree, help him out and basically ask nothing else of him, though he does offer his aid. So I take him up on that. We run around, make some money (party banter happens) and then I return the favor he gave me by almost getting him killed in the Deep Roads. Three years pass and you can assume that things happened. We talked and such, natural things. And then I help him kill his hunters and listen to his troubles, and THEN we get to the romance. Which, for him, is difficult. My poor heartbroken Hawke is, well...heartbroken, but she remains faithful. So by the time he admits he loves Hawke (though I don't think he ever actually says those words) it's been years, and I can believe it. It's not fleeting, not casual, not flighty. It's been with both of us for years. It's...more real...for lack of a better description...
Just a little observation, because I should be studying but I can't. DAII has ruined my academic career...only for the moment though. I'll get a hold of myself in another week or so.