If there's one theme running throughout all the Superman movies, it's not something like "justice will prevail" or "protect the innocent" -- it's "relationships suck, and you should never even bother with them." Seriously, in these movies, if Superman so much as goes half-mast looking at a lady, you know something terrible is gonna happen.
Take Lana Lang, Clark Kent's high school sweetheart and romantic interest in Superman III. Superman's attraction to her gets him to come to a parade in Smallville, where he's exposed to the kryptonite that makes him evil. Later, he almost lets a man fall off a bridge because he's too busy hitting on Lana like a creep.
"Have you ever snorted coke off invulnerable buttocks?"
There's also the time Clark dated his boss: not Perry White, but Mariel Hemingway's character from Superman IV. Clark's feelings for her translate into his dimwitted radioactive clone having a psycho crush on the same lady, which gets her kidnapped. She probably got some type of skin disease for being alone with the guy for five minutes.
And then, of course, there's Lois Lane. When she and Superman first hook up in Superman II, a talking hologram of Supermom (or Superdad, depending on which version of the movie you're watching) flat out tells Superman that he can't be with a woman and protect humanity, because "the concepts are mutually exclusive." Apparently, you can't have a girlfriend and be good at saving people at the same time.
"Superman, we can't control this fire!"
"Hm. Probably because you're all married, losers."