Not weird at all, just looking at things through different glasses.
Me, I tend to think about stories in the long-term. I'll read a story and then I might spool out in my head the time after, thinking about how the characters might develop or end up. "Firsts" and "perfection shattered" always affect me greatly in reading, as well. So I can't help but think after reading, for example, that no matter how happy the characters seem to end up, if the couple's first time in the sack is violent or for all the wrong reasons, that's what they remember whenever they reminisce about it - violence or pain or embarrassment - and that they'll regret that they didn't make a different start.
We don't usually forget the first time significant things happen and the memories can be beautiful or they can be sources of pain for the rest of our lives. Add to this thinking my tendency to follow the story mentally past "the end" and you can see how I can take a seemingly happy ending and find the melancholy in it.
Anyway, those are my glasses and how I wear them. I know everyone doesn't look at these things the same way, but I did want to add my two cents for the sake of the discussion. I certainly prefer a happy ending after dark middles! *g* I can see both (dark endings and dark middles/happy endings) as darkfic.