请问“我在暗恋他”用英语怎么表达？

have a crush on sb
I have a crush on her.

最简单的方法： I like him/her, but he/she doesn't know.

I am falling in love with her secretly!

He/ she is my secret love.

暗恋 - Secret crush, 长长被简称为 crush
暗恋着xx - Secret crush on xx
暗恋者 - Secret admirer
I secret crush on him

I have a crush on him.