In fact I would say that friendship is as hard to handle as love is, or even marriage.

1. 为什么是 love is，这样后面难道不缺少表语么？

【答】friendship is as hard to handle as love is (hard to handle). 比如：

Tom is as eager to go as John is (eager to go).

2. 为什么 marriage 后面没有 is，并列连词 or 不应该保持并列结构的对称么？

【答】or even marriage 后没有is，是为了简练而省略了，也可以加上。

【翻译】事实上，我要说友谊跟爱情一样很难处理，甚至婚姻也是如此。