I wouldn't say they where each others true love because that implies romantic implications and also taht xander is willows true loves when we all know its tara. They have an unconditional love for each other but only as friends. There thing in series 3 was lust not love and my own personal theory for why that happened is divine intervention i.e. jasmine cant control love so made them lust for one another leading to the breakdown of xander and cordys love relationship meaning it was easier for cordy to go to L.A. because she had noone to stay for