If a man or woman is very insecure in a relationship and feels threatened by casual friendships or coworkers as potential sexual rivals (and it isn't anywhere like that), then that person is not a stable partner with whom you can have a solid long term relationship - and there is risk of abuse to try to keep the partner there, both physical and emotional.
If one partner flirts with strangers in order to make their partner feel jealous, that is emotional abuse. The partner should only flirt with their own partner. To flirt with others and get a thrill that strangers find them attractive IS a violation of the relationship and can lead to adultery. Which is why it is absolutely wrong to try to create jealousy in one's own partner when it doesn't exist.