As Shakespeare wrote, the course of true love never did run smooth. Which is perhaps just as well for tales of romance, which would be rather dull without the drama of lovers having misunderstandings and struggling to overcome barriers that keep them apart.

【翻译】正如莎士比亚所写，真爱之路永不会是平坦的。这大概也适用于爱情故事，如果没有恋人之间的误解，以及克服彼此之间的隔阂，浪漫故事就会相当乏味。

从句子意思看，两个 which 引导的从句都是“非限制性定语从句”。两个which 都是指代前文整个句子的内容。按语法规则，不应单独成句。但是，which 单独成句的情况还真有，以下是语料库中的句子。

Which is how I remember what happened. 

这就是我怎样记得发生了什么。

Which is what we have here. 

就是我们在这已经有了的。

Which is why I started meditating. 

这是我开始学习冥想的原因。

Which is why an article like this can be transformational or worthless – it all depends on you. 

这也是为什么像这样的文章可能被转化，也可能一文不值——这都取决于你。

Which is why the book was so important. 

这就是为什么那书是如此的重要。

Which is why I generally choose to do something rather than own something. 

这就是我通常选择去经历一切而不仅仅以拥有为目的的原因。

Which is why I have always purchased apple products and admired you. 

这就是为什么我一直购买苹果产品和仰慕你的原因。

Which is why I sometimes go into the garden and insult the weeds. 

这就是为什么我有时会去花园辱骂杂草。

Which is exactly what we did. 

那就是我们当时所做的。

Which is how most of us go through our day. 

这便是我们大多数人过的生活。

关于of lovers having misunderstandings and struggling， 不是“动名词复合结构”。having misunderstandings and struggling 是现在分词短语作定语，修饰lovers.

同意刘老师解答

As Shakespeare wrote, the course of true love never did run smooth. Which is perhaps just as well for tales of romance, which would be rather dull without the drama of lovers having misunderstandings and struggling to overcome barriers that keep them apart.

参考译文：就像莎士比亚所写的那样，真爱的的路上永都不会是进展顺利/一帆风顺/平坦的。这大概也对浪漫爱情故事也是这样，如果剧情没有恋人之间的误解/误会，以及克服彼此之间的隔阂/阻碍，浪漫故事将会相当乏味。

run smooth 进展顺利

The course of true love never did run smooth.  

真正的爱情总不是一帆风顺的.

He has run smooth in the last few years.  

近几年来他发了财.

The course of true love never did run smooth. 

真诚的爱情之路永不会是平坦的. 

The course of true love never does run smooth.  

至爱无坦途.