The only problem? That would be prohibited by Air Force protocol as one is a colonel and one is a captain , so the writers came up with a clever workaround to still tell the story they wanted to tell.
That's not why they can't have a relationship. It's because they're in the same chain of command.
2.2.2. All relationships, whether pursued on or off duty, are prohibited if the relationship:
2.2.2.1. Compromises, or reasonably appears to compromise, the integrity of the
supervisory authority or the chain of command.
2.2.2.2. Causes actual or reasonable perception of favoritism, partiality, or unfairness.
2.2.2.3. Involves, or reasonably appears to involve, the improper use of grade or position
for personal gain or demonstrates the abandonment of organizational goals for personal
interests.
2.2.2.4. Is, or is reasonably perceived to be, exploitive or coercive in nature.
2.2.2.5. Creates an actual or reasonably foreseeable adverse impact on good order,
discipline, authority, morale, or command’s ability to accomplish its mission.