He is the 7th house and any potential partner is the 1st (being the turned 7th). No aspect or contact between Mars and Venus, so I'd say "no" he's not cheating. Him being in the 5th just shows his intentions i.e having some fun.
His 5th house ruler aspects him but that is prohibited by Mercury, so it means little. Added to this, the Moon is Void of Course, showing nothing coming of the situation.
Again, I don't think he is cheating or that he will on this trip.
EDIT: I forgot to mention that the antisca of Mars is just inside his house, showing that he is thinking of only himself on this trip. For me, another indication of a "no".