I can understand your kissing a pretty model, but your giving money to an ugly one -, no!

but在此为并列连词，表示转折。并不是修饰动名词复合结构。其表达的意思是but your giving money to an ugly on, I can't understand it at all. but连接并列句，动名词短语为左偏置结构，其强调作用，在第二分句中用it指代。偏置结构主要用于口语。

动名词为动词性结构，通常被副词修饰，不能用形容词修饰。如果一个doing形式被形容词修饰，这个doing是名词化的动名词，不可后接宾语。例如：

I hate his quick talking. 名词化的动名词，被形容词修饰。

I hate his talking qucikly. 动名词，别副词修饰。

I liked his nice playing of the piano. (正确。名词化的动名词被形容词修饰，宾语由介词of引出）

I liked his nice playing the piano. （错误。形容词修饰的是名词化的动名词，不可后接宾语。要么改为副词修饰，要么宾语由介词of引出。）

I liked his playing the piano nicely. (正确）