I am still involved in law enforcement. I work part time to keep my license active, just dont get paid for it anyway, if she is getting involved with a police officer, you need to expose it. Depending on department policy, a lot of departments discourage anything like you are saying, they want their officers to be upstanding with morals and ethics. I say rock his world through his employer, It sickens me when people mess around with married people.
If he tries to use his powers, in my state that is considered offical oppression which is a felony. Law enforcement cannot use their authority to threaten or cause anyone harm outside of enforcing the law. Depending on your state most states do have some law in place for such actions. If he tries document it, report it and expose the pr!ck.