All the water signs: Cancer, Scorpio and Pisces, can be possessive and jealous and it's tied up primarily with emotional attachment. Pisces is probably the least jealous of the other two and generally feels empathy and compassion for a lot of people. Taurus is another sign that is known for its need to possess physically (earth), and has a deep need to feel secure. Possessiveness derives from insecurity and therefore triggers the need to maintain (fixed) stability. Taurus can be extremely territorial around a partner, and may view them as a belonging, and expects total loyalty and fidelity and is unable to abide anything else.
Scorpio has long been known for morbid jealousy, arising from his deep suspicions, and the 8th sign of the zodiac fears abandonment and emotional betrayal and needs to form close bonds with a select few. Another sign known for its jealousy, is Leo. The king of the beasts hates betrayal of any kind and takes it as a personal insult. The least jealous in the horoscope are most definitely the Air signs, they seem to be happy with friendship and to keep things well ventilated, allowing freedom and movement of expression. However, according to C.E.O Carter Essays on the Foundations of Astrology "Libra appears to be jealous because they need to be liked. Mirror, mirror on the wall who's the fairest of them all!" It would never turn into the real pathological jealousy of the other signs, and has much to do with likability. All the fixed signs possess fixated natures and find it hard letting go of a loved possession, emotions, loved ones and ideals. The exception being Aquarius (Air) and they need to feel liberated, likes to be involved in friendship and wants space and can hold others at a distance. Perhaps Aquarius would find it hard letting go as friends and wants to maintain the relationship in this way.