Most Helpful Girl
Not at all, my ex was very shy and because of it he was always looking for a chance to have sex. I thought it meant he would be nicer but when I wouldn't have sex with him and another girl showed some sort of interest he immediately went for it and waited until a month later (conveniently, the day before my birthday) to brake it off and try to persue a relationship with her instead.
Most Helpful Guy
You couldn't accurately say that until or unless they were given the same opportunities to cheat. If their shyness denies them of those opportunities it doesn't mean that they are more faithful in intent.
The most likely truth is that people with a higher level of integrity are more faithful, regardless of how outgoing they are.