Given the original question was about the rules, not the interpersonal relationship dynamics between the two competitors, I would ask how well the rules were defined between the two players, without the nuances of their romantic entanglements being a factor?
I suggest that if "Standardized Rules," "BCA" or "APA" rules were in place, different answers to his question might apply.
Then too, the level of the game and its rigid adherence to rules is usually a gray area - typically dependent on the amount wagered (be it money or something with value e.g. dinner out) - or, if no value is assigned, merely bragging rights...
In addition to the written rules, which when silent allow for nuances to be deployed, we have commonly accepted practices that need not be discussed, simply accepted. For example, if the GF had the 8-ball 3" from the center-line of a pocket - and the CB 6" from that, in a straight line, "calling" that shot (assuming the opponents remaining balls pose no possible interference) I believe the rules suggest calling the shot before execution is unnecessary.
Here's the quoted rule (from this website) that supports my notion of why the shot need not be called - even if "CALL SHOT" is adopted:
"In Call Shot, players need not call obvious balls and pockets, however, it is the opponent's right to ask which ball and pocket are to be used in the shot if they are unsure of the shot. Bank shots and combination shots are not considered obvious, and appropriate care should be taken in calling both the object ball and the intended pocket. When calling the anticipated shot, it is not necessary to indicate details such as the number of cushions, banks, kisses, caroms, etc that will be used in the shot."