that's is the usual excuse - "friend hp low battery, used his hp".
you can stop him for this trip, but he can go other trip discreetly. Since you have details of this trip why not do a checks whether he is going up with that PRC. you will get your answer fast and accurate.
What i feel is that you should let him go and get a PI to check on him. If there is a women, get the evidence. if really there is not, then you have to tell yourself to strat trusting him.
If you are looking for a good PI, you CAN pm. i know of a good PI to recommend.