Why do some people find it so difficult that a person remains faithful to the one they love no matter what?

it could be a couple things honestly, 1.) it could be the fact that they don't like the person and they cannot see why you do either. 2.) they could not understand the true meaning of love, and are "immature" in that subject of life. or 3.) and probably the most common: they're simply jealous. don't mind these people, they're evrywhere, just stay with the person you're with and love them forever, as i type im sitting next to the love of my life. and i love it =)