PLD use their cure spells to build up hate. Anyone telling you not to heal yourself until the main healer is running low on MP has no idea what he or she is talking about. Your responsibility is to keep yourself alive and build hate while doing it. Tell the WHM to slow down on the cures so you can have a chance to heal yourself more often. Also, healing other party members isn't forbidden. Throwing out a cure II or III when hate has turned onto another player not only helps the player that got hate by curing him, but also builds more hate for you. Healing oneself and occasionally others is what makes PLD a worthy tank.