I am asking this question ahead of time and am seeking advice on a specific situation.

My LTR is just finishing school and her placements. Next week is her last week before she is done and we are going on a trip to the Caribbean after this.

However her responsibilities include training the next person to take her place when she leaves. The person she is training is a guy who goes to classes with her and is someone who I know would like to get with her. I know not because my LTR told me, but because I am a guy and know that every guy wants to fuck a hot girl.

Now she has never really mentioned this guy and just casually brought up the fact that she has to train him before leaving. Furthermore she has not displayed any red flags or given me any indication that this guy is on her mind at all. Her classmates are always planning drinking nights out and she does not join them as she prefers to be with me and join me on nights out.

Critical to all of this is the fact that before entering our LTR she told me how guys and girls cannot be friends and she would not be comfortable with her BF going out alone with another girl. I agreed and this is one of our rules for the relationship.

Now seeing as she will be spending time with him for training at her placement I suspect that he will try to ask her to join him for lunch during this time. If it is a group thing I would not care, if it is just her and him it would be a violation of the rules we established before entering this LTR.

Now my question is this, should I reiterate this to her before next week (through example or stating it directly)? My plan is not to say a thing, and if she brings it up to remind her what we agreed to before.

For example if she were to call me during the day asking me if it is okay what should my response be? Should I say "you do not need my permission to do anything" or "we agreed that going out alone is not acceptable"?

If I do not say anything and she goes out to lunch with him and tells me after the fact it would be a hard next situation for me. If this is the case I plan on breaking up with her on the spot and cancelling our trip.

Since the consequences for this are harsh would it be worth it to say anything beforehand or just let her make her own decisions and if she makes the wrong one then we go our separate ways.

My feeling is that if I bring it up it can make me appear needy and insecure, but at the same time if I don't say anything I am not being clear in telling her that this is a nextable offense. My go to is to see how things play out and let her dig her own grave if she is stupid enough to do so. However if she tells me that she went out to lunch with him after the fact it will already be over and I may feel like I should have spoken up before the fact.

On the other hand if she does this without seeking explicit approval from me before or does not just reject him herself then she is not a girl worthy of my commitment anyways and this would justify my decision to leave her.

Let me know what you think and if you have any relevant experience.

EDIT: I plan on providing updates next week if there is a need to.