The Romance:
Let's face it, any other guy who had his eyes on Lois Lane never stood a chance. She was seeing a tall, good looking guy with a chiseled frame and, oh yeah, he could fly and bench press several Mack trucks. It's kind of hard to compete with that, and even harder to compete with a guy who can fly around the world so fast he actually reverses its rotation, sending everything back in time in order to save her life. That makes your roses and box of chocolate look like a big pile of shit.
Wait, Something's Not Right Here...
You'll probably remember that one of the catch phrases they always use to introduce Superman, right after all the "faster than a speeding bullet" stuff, is "strange visitor from another planet." You know, as in, he's not from Earth. As in, he's not a human being.
Sure, he looks like a human man, thanks to whatever one in a quadrillion coincidence of evolution caused life on Krypton to look just like ours. And he's got a presumably working humanoid dong, but that doesn't change anything. Lois Lane fucked an alien.
Like this, only a little less furry.