A relationship is based on the solid foundation of trust and understanding. However no relationship is devoid of jealousy or possessiveness. Sometimes the girl in the relation is possessive, sometimes the guy is. Is it a sin to be jealous? No.
Does it mean that the person being possessive is a psycho? No! People have different personalities and natures.
Some are more easygoing and trusting, whereas others are more dubious and skeptical. This is not due to a personal choice; it can be due to previous experiences, upbringing or other factors in life.