>>51056331Gardevoir's first egg group is Amorphous, remember. It's not unlikely that a telepath with a pliable body might start shifting their shape to better suit their partner's needs and desires.
In other words, Gardevoir may very well start growing more curvy to foster their trainer's interest, but it's also a dead giveaway to everyone else that they have, at the very least, been thinking about their Gardevoir in a lewd way.