We have all experienced jealousy in one way or another and I think we can all agree is sucks all the way around. If you are jealous of someone, you feel crappy inside and if someone you care about gets jealous it can make you feel crappy too.
Sometimes it feels nice to know your partner is jealous, it can be a little reassuring, it's when the jealousy becomes extreme, toxic and abusive that you begin to lose your attraction to your partner. And the relationship fails.
Couples need to first work on their own confidence and self-worth before entering into a trusting relationship. You have to know your own self-worth before you can have a healthy relationship with another. But hey this is not always the case, we fall in love first and think I can work on this or that, and sometimes we do and sometimes it does work out. But first it takes a whole lot of self-reflection.
Extreme possessiveness is jealousy at its worst. It could lead to stifling your partner and not allowing normal human interactions other than being with you. Disallowing any 'me' time to your partner, grudging your partner's healthy friendships and at its worst, suspecting your partner unduly and engaging in unwarranted conflicts which create strain in the relationship. Such unhealthy jealousy destroys relationships and needs to be transcended by the one experiencing it.
Mutually affirming and appreciating each other is important. One should try and have some shared activities and interests along with individual pursuits, with a healthy balance of 'we' time and 'me' time. Paying attention to each other while socializing and making each other a part of one's individual successes by sharing the process and the achievement with each other are small things but can mean a lot to the relationship.