Super powers ladies man and total boss have in common with a nerd someone denied by society and not very interesting a lot. Superman the man of steel not attracted to the opposite sex. That the fact that Superman has never married Lois Lane is out of the question and it just automatically makes the man of steel a homosexual. The Occurrence that Superman is not immortal because that would be unrealistic to society and would make the masses want to read the comic less than what the intended writer would want.
On a positive side Superman's hidden disguise as Clark Kent has a symbol behind it not only is it the main reason for him being the person he is and falling for Lois in the first place but it symbolize the average cast out male of today's society for example jocks and nerds making Superman to apply to all types of masses even orphans.
In opinion reasons proven by actual fact why that Superman doesn't marry Lois Lane is told to her in many episodes and that reason is that he doesn't want to put her in danger so they cant be together in the way that's is a given fact but what happens later on Lois finds out that Clark is Superman and she eventually marries Clark Kent.