unable to think clearly or behave in a sensible way because you are in love with somebody, especially somebody who is not in love with you 害相思病的（尤指单相思的） He’s been wandering around all week like a lovesick teenager. 他像一个相思病的少年一样整周徘徊。
Oxford Collocations DictionaryLovesick is used with these nouns:- teenager