The eternally faithful moodlet should come back once you get home, if you have them be romantic in public again, that's what I've found happens.
The game treats the locations differently, to the French who don't know them they are not eternally faithful but if they spent enough time kissing in front of them they might decide that they are, I've had it appear while on vacation before now.
As for the pop up, once again I would say have your couple be romantic with each other to make sure their gender preference is set for male and the women should stop firing off messages, the men might start though
When you travel the game copies your sims to the Export.DB file in your save folder to put them in the vacation world, and when you go home it does the same again so the ones that arrive back have all the info, items and so on from the vacation, but some info gets left out such as gender preference which is why your sim got messages from females, I've had gender neutral sims get messages from both sexes before now.