相亲相爱的英语是"fall in love"。这个短语来源于英语的中世纪语言，其中"fall"表示"降落"，"in"表示"在"，"love"表示"爱"。因此，这个短语字面意思是"在爱中降落"。

例句：

1. They fell in love when they were young.

2. She fell in love with him at first sight.

3. He has fallen in love with her.

4. They are very much in love.

5. She is deeply in love with him.