Amongst peers interpersonal relationships were tolerated as long as it was quiet and strictly kept off ship. That said, long term relations did not often happen and it was normally a very short thing.
Relationships breaking the commissioned / non-commissioned barrier, however, were massively frowned upon, as well as ones between direct line managers and subordinates. A good way to kill a career! The superior would open themselves to allegations that s/he could be abusing their position, certainly with far younger and less experienced people in subordinate roles. It also could offer a breakdown in discipline. Then we enter the dangerous world of boards, panels and hearings.
Regardless, those in relationships would find themselves posted elsewhere to prevent bad situations – what if the superior had to discipline the junior? What if the superior had to order the junior into a dangerous situation, such as fighting a fire? Would the concentration of both in a critical moment be impaired if they knew the other was in danger nearby?
Each situation would have to be judged on its merits. In training, it was well known amongst us sprogs that one of the Lieutenants training us was in a relationship with a Marine Sergeant. They were both instructors in different departments and it was never seen in public, so not a lot happened and it continued. If that Lieutenant or Sergeant had formed a relationship with a cadet under training however, the establishment would have dropped on them (and the cadet) from a great height. I think what I’m trying to say is that’s not so black and white as “NO RELATIONSHIPS ALLOWED”.
To put this back on topic – would Simms be in the wrong to have a relationship with Laporte as her direct line manager? Probably. If not for the operational side being so intense and demanding on his time, I would suggest the Captain of the Indus or his senior officers would eventually intervene (although Simms ended it on her own terms before anything really started). Would it be different if they were pilots of similar rank in different units? I think it would be tolerated. I think that such a relationship adds depth to both characters, and allows massive potential in terms of drama - let them challenge the rules and get court martialled! Or have a situation where they have to choose between their relationship and their military objectives! For me, the fact that they are same sex is not relevant, the story is still good either way.