In the golden age of superheroes, marriages were relatively infrequent among the main characters. As most stories were serialized (there was little continuity between individual issues) other factors became more important in the presentation of characters. For many the underlying romantic tension was far more important than seeing a resolution to that tension. Additionally in the early years of comics, a common theme was a character being loved as a hero but ignored as their secret identity (which they still had to struggle to maintain.) This made it such that marriages were not presented often in comics. Additionally due to the serialized nature of comics it was unlikely to have a wedding issue which ended with two characters actually being married (though weddings were often used as a plot device.) Regardless the underlying desire for marriage was still a strong driving factor for many characters. For instance, the golden age Wonder Woman said that she would finally marry Steve Trevor once she had eradicated crime forever.
The 1960s and the beginning of the silver age saw a different interpretation of marriage, though still similar to the golden age. By this point superheroes were no longer dominating the format as other genres such as romance became more popular. Marriages and weddings were a common theme in romance comics, but they were shown still as in the golden age either as a plot device where a wedding wouldn't happen, or as the resolution to a self contained story in a romance setting. With the development of the medium in the silver age to be one more geared towards adults, the presentation of relationships changed. Now notable characters such as Hawkman and Hawkwoman, the Elongated Man and Sue Dibny, and Mr. Fantastic and the Invisible Woman were all displayed as being in long term marriages.
Since the 1980s, comic book weddings have tended to become minor company events with the marriage serving as a vehicle to join both heroes and villains together. Generally the more popular the hero, the bigger the events. They often are standalone issues as well separate from the main series. One of the highest profile weddings in the continuity of comics as well as from a contextual standpoint was the wedding of Peter Parker to Mary Jane Watson in the Amazing Spider-Man Annual #21 in 1987. While this ended almost two decades of romantic pursuit between the two characters, it also set the precedent which many wedding issues have followed since (to incorporate at least in some way the appearance of villains who aim to foil the wedding, either deliberately or unintentionally).
Marriages in Comics