Intel points to a possible invasion of Earth by unknown forces. This is a time for the Legion to be at full-strength not for four Legionnaires to quit!
Legion leader Brainiac 5 is royally cheesed that Saturn Girl, Lightning Lad, Ultra Boy, and Phantom Girl are too busy being in love to pay attention to his updates about the possible invasion. He acts like a real jerk towards the four love birds. His attitude doesn’t improve when the four decide to marry (coupled up, not all four together) and, according to the Legion Constitution, are forced to resign from the Legion.
As you might have guessed all this Sturm und Drang is actually planned by Brainiac 5 and Saturn Girl. If the two couples married and quit the Legion Brainiac 5 would have to schedule tryouts to fill the gaps in their roster created by their departures. They theorized that alien spies would try to infiltrate the Legion by pretending to be prospective members. Seems like a long shot to me but hey, what do I know?
Rules 1 and 2(b) of my Grand Unifying Theory of LoSH Asshole Behavior™ apply here. Brainiac 5 is pretending to have a stick up his ass over the romantic relationships so that the four Legionnaires could pretend to leave the Legion at the worst possible moment. But we all know (from rule 3) that no one is pretending. B5 is a dick and the four Legionnaires are acting like lovesick idiots.
Because Brainiac 5 has a cold, unemotional computer mind.
On my Legion Jerk © scale this issue gets a:
The 3 spies Legion prospective members:
