Sounds like perhaps an affair is going on here. Hell hath no fury like a woman scorned.
I was scrolling through the comments and had just thought the exact same thing, when I came upon your post. It was the very first thing that came to mind.
Yeah, sounds like some hanky panky. Probably come to find dozen S/S folks all tied into this.
From my POV I'd say YOU are CORRECT, it's most likely an AFFAIR.. her actions are that of a "woman scorned'.. and the fact the other agent made NO retaliatory effort pretty much validates what you said.
Sounds like perhaps an affair is going on here.
My thought.