“...almost always the affair involves an officer and his/her subordinate,”
In the cases I mentioned, only one involved fraternization; the others were adulterous relationships with civilians, with another member’s wife, and such.
The Lt Gen was notorious for flying his military aircraft halfway across the country several times a month to meet with his mistress (ostensibly to meet with one of his remote units). It continued until the Maj General I worked for (at the base he flew to), refused to let it go.
Yep. That will do it every time. I wouldn't be surprised if a stunt like that not only ended a career but also ended with a little brig time.
To your original point, these things are prosecuted from time to time when it's not a fellow service member who is the "other party". Your personal experience notwithstanding, I'd estimate that few than 2/5ths of these prosecutions involve non-military "parties".