What is the difference between jealousy and envy?

They are distinct emotions that plain usage conflates, and the difference is about how many people are involved.

Envy involves two parties. You lack something another person has, and you want it. Envy is about a possession, quality or achievement — their job, their talent, their house, their ease with people. The structure is: they have X, I do not, I want X.

Jealousy involves three parties. You have something — usually a relationship — and fear losing it to a rival. The structure is: I have a relationship with A, B threatens it, I fear loss. Jealousy is about protecting rather than acquiring.

So you envy a colleague's promotion; you are jealous when a partner seems interested in someone else. Using "jealous" for the first is ordinary English and technically imprecise.

What each involves emotionally:

Envy carries inferiority, longing and often shame at feeling it — which is why it is rarely admitted. Researchers distinguish benign envy, which motivates self-improvement and is directed at closing the gap, from malicious envy, directed at pulling the other person down. The first can be productive; the second is corrosive.

Jealousy carries fear, anger and threat. It is more socially acceptable to express, and in some framings even treated as evidence of caring — which is where it becomes dangerous, since possessive and controlling behaviour is frequently justified as jealousy.

On jealousy in relationships. Some is common and not in itself a problem. It becomes a problem when it drives monitoring, restricting contact, demanding access to devices, or accusations without basis. These are controlling behaviours, and they are recognised markers of coercive control rather than affection.

What helps: naming which emotion it actually is, since the responses differ; addressing the insecurity rather than the trigger; and treating a partner's monitoring as a boundary issue rather than a compliment.