Key difference: a Lover is a person who is in a romantic relationship with another person. Mistress is a woman who has an extramarital relationship with a married man.

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A lover is a partner in a romantic relationship. A lover is also defined as the person who is in love with another person. Lovers are two people that will be together until the end of time, who love and cherish one another's feelings and thoughts. Two people who are truly and deeply in love and can't stand being apart for too long. Two people who need each other every day, every minute, and every second. The relationship between the two lovers is very intimate. The two lovers in a relationship love each other unconditionally. A true lover accepts the other person for who they are. A lover completely denotes his everything for the other person and can do anything to make the other person happy. Love has no boundaries. A lover is a title given to a person, to whom one is committed. He is infatuated and addicted to the other person. A lover expects nothing in return from the other person. A lover does not expect any financial rewards or material rewards from the other person. A lover just might be the person they may be married to. The relationship is kept social. A lover may at times also have an affair with a married person.

Also see: Crush Vs. Infatuation

A lover may also mean a person who likes or enjoys specific things; there are food lovers, animal lovers, music lovers, etc. A lover might be a devotee, fan or follower of a band or a person. He can also be an aficionado – a lover of some musical genre or performer. A lover is also a follower, a person who accepts the other person's leadership. An aerophile is a lover of aviation.

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A mistress is a woman who has an extramarital affair with a married man. She is the female lover and companion of a married man. The relationship is considered to be semi-permanent. It is usually kept a secret. At times, it may imply that the mistress is ‘kept’, it just means that the man is paying the living expenses. In ancient times, a comfortable or a lavish lifestyle was maintained by a wealthy man, so that the mistress was available for a physical relationship. Such a woman would be called a mistress or a courtesan depending on the environment. In modern times, a mistress is referred to the female lover of a married man. Historically, if a man kept a mistress, it implied that he would be responsible for paying her debts. He had to provide for her as much as he would for his wife, even though he was not legally bound by law. Later on, mistresses started becoming financially independent of man. There is an emotional and social relationship between a man and his mistress. There were times, where the men would leave their wives for their mistresses.

See: Difference between lover and beloved 

Difference between Lover and Mistress:

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