"fall in love" 后面 可以加名词（sb.）或动名词（doing sth.）。例如：

1. I fell in love with her at first sight.

2. I fell in love with playing ping pang.

3. I fell in love with it as soon as I arrived in Shanghai.

虽然 "fall in love with sb./sth." 是一个常用的英语短语，但 "fall in love with doing sth." 相对来说不太常见。如果需要表达爱上做某事，可以考虑使用 "I'm addicted to doing sth." 代替。

总结：

"fall in love" 后面可以接名词（sb.）或动名词（doing sth.）。

"fall in love with sb./sth." 是常用的表达方式。

"fall in love with doing sth." 不太常见，可以考虑使用其他表达方式。