It seems natural for people in my culture to get jealous when someone of the opposite (or in some cases same) sex shows interest in our mate and vice versa. Was just talking to a close relative who told me he and his mate get along fine at home but each has a problem when they see the other getting along with a perceived competitor. Of course each person has their own jealousy index but who has a zero? Maybe some people, especially in other cultures. So most of us with observant mates need to be careful with what we say and who we look at too long and so forth. In some more extreme cases it's best to indicate no interest at all in speech or deed in someone who might be considered to be attractive. I wonder to what extent was the burqa inspired not just by men's not wishing others to look at their women but by women's jealousy, not wanting their men to be attracted to others - therefore, cover them all. When I wrote 'their women" I was aware that this indicated possession. In a sense we are each the property of our significant other. Sun Myung Moon, whom I don't usually quote, taught that a husband and wife are the owners of each other's genitalia.
The most extreme case I know of is a bi-sexual couple who were both so infected with jealousy that they couldn't look at, talk to, or mention anyone between puberty and octogenarians. They couldn't watch any TV or movies, live in a city, or have magazines. They got jobs in orphanages and old folks homes but there were staff and visitors to deal with. Finally they had a stroke of luck when she won a gigantic lottery prize. They had their eyes surgically removed and moved to a posh hotel suite. But then they noticed how attractive the voices on the radio and of the staff were. The hotel instituted a policy of communicating with them through a robotic voice that neither found attractive. They created a blog which quickly had many followers, especially among blind deaf mutes. The harmony they had found was appealing to others who created a secret cult around this couple. They moved from the hotel to a commune founded on their principles and had their hearing surgically terminated to be at one with the others. They could only tell one-another apart by feel and smell. Eventually the barriers broke down and no one thought about that jealousy thing anymore. Last I heard they were one big happy group grope.