Not a hard concept to understand or do! If someone wasnt faithful with you, they didn't love you. They didn't care about breaking your heart. When you truly love someone, being faithful & trusting someone is the most natural thing.
When you love someone. truly love them friend or lover, you lay your heart open to them. You give them a part of yourself.that you they can hurt. with a map of where to cut you deepest and most painfully on your heart and soul.