英文中的「lover」不是中文中的「愛人」,而是「情人」,且多用於女人婚外的情人。男人的婚外情人是「mistress」
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Someone's lover is someone who they are having a sexual relationship with but not married to.
――Collins COBUILD
lover是不分男女的,就是情人,現代英美社會最常用,boyfriend和girlfriend也常用來指這種關係;男人的情人可以叫「mistress」,但這是個蠻古舊的詞,除了一些歲數很大的人,現在一般很少
用。第三者,也常說成「the other person」
搞婚外戀,美國人常說成,「have an affair」、「cheat on someone(one's spouse)with someone else(the lover)、「commit adultery」、「have an adulterous relationship with someone」等等等等。
a person who loves or is loved
fan: an ardent follower and admirer
a significant other to whom you are not related by marriage
wordnet.princeton.edu/perl/webwn
An intimate relationship is a interpersonal relationship where there is a great deal of physical or emotional intimacy. It is usually characterized by romantic or passionate love and attachment.
en.wikipedia.org/wiki/Lover