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All Pokémon of the Ralts line will form a deep bond with their trainer or master. However, this bond manifests differently.
A master that radiates negative emotions like hatred, rage, despair or even murderous intent for long periods of time will wear down a Ralts morale and health, and cause it great discomfort, to the point where the Ralts may attempt to escape, if its attempts at helping its master go fruitless.
Something similar happens with Kirlia, though a Kirlia pushed too far may lash out, sometimes violently.
Gardevoir is unique, as negative emotions will influence it. A trainer corrupted by evil thoughts will corrupt its Gardevoir eventually. Their loyalty and bond is unconditional, and the Gardevoir will put its masters orders before its own thought. "My master, right or wrong". For this reason, properly caring for a Gardevoir requires a great deal of maturity, responsibility and a strong sense of ethics and morality, as the master must understand that their actions deeply affect their Gardevoir for better or worse.
Gallades are similarly extremely loyal, and consider dying or being extremely injured for the sake of someone they respect is the highest honor possible for them. This kind of devotion to duty has "drawbacks", a Gallade might disobey (and question its respect for its master) an order to "stand down" if this order means abandoning innocents to their fates while the Gallade has reasonable chances to save them. Similarily, a Gallade pushed into committing atrocities, crimes, or dishonorable combat will have very little problem with turning against its master.
For this reason, Gallades are heavily favored by militaries or mercenaries who have strong ethics and desire minimizing collateral damage, as they make excellent and reliable allies. Gallades are similarly highly in demand for security and bodyguard work.
