Now, a person who's compromised by literally being in bed with a spy has even more pressure not to disclose the relationship, providing another avenue for blackmail.

Ehh not really another avenue for blackmail. They have a special hotline just for people in situations like this, minimal punishments as long as you didn't willingly cooperate and promptly and fully report it all with details of people, time, place, etc. They disappear you for a short while to attempt to prevent the enemy from using any blackmail they have but its witness protect not Gitmo.

The thing US spy agencies learned decades ago was just this risk and they took steps to have internal services and solutions to allow escape valves so it wouldn't work. They're not completely incompetent. In fact it's only in the past 5 years that China itself has established similar leniency for reporting the problem systems to deal with their own issues of western spies and blackmail.

Now might it keep them from reporting contacts to prevent getting in trouble and that hurting US mapping of Chinese counter-espionage/honey-pot networks and such if they want to continue the relationship? Sure, absolutely. But it's not going to provide for trapping anyone in any deeper who's fine with breaking it off.

Even in situations where the person ISN'T sleeping with a spy, it creates an avenue for blackmail. One that will cause internal turmoil between staff members who know their colleague slept with that girl on the night out the other night, and also by external operatives if they discover it.

Honestly the harmful office politics of it is going to be non-zero. Everyone knows when someone is dating someone or when something happened when out drinking on the work night, and there are work colleagues that have 1 or 2 work friends outside of work... Especially when in a foreign country with few options for English speakers.