love affair
noun uk/ˈlʌv əˌfeər/ us/ˈlʌv əˌfer/
[ C ]私情，风流韵事;（非夫妻间的）性关系
a romantic and sexual relationship between two people who are not married to each other
[ S ]挚爱，热爱
a strong liking for a particular activity or place
Her love affair with ballet began when she was ten. 她10岁的时候开始爱上了芭蕾。