1. 风流韵事；（非夫妻或同居情侣间的）恋爱（或性）关系
A love affair is a romantic and usually sexual relationship between two people who love each other but who are not married or living together.

2. 极大的喜爱；强烈的的兴趣
If you refer to someone's love affair with something, you mean that they like it a lot and are very enthusiastic about it.

1. a relationship between two lovers

Synonym: romance