Many of these individuals were faithful for years, sometimes decades. They seem to be well

balanced, mature, caring, anddeeplyinvestedin their relationship. Yet one day, they crossed a line they never imagined they would cross. For a glimmer of what?

问题：

invest 在文中是不是为及物动词？省略了什么宾语？

刘老师的解答是正确的。

本句中，deeply invested in与前面的well balanced, mature, caring并列，都是 不定式to be的表语。所以invested是及物动词invest的过去分词演变而来的形容词，虽然词典没网站收录这个形容词。

《韦氏学生词典》invest作及物动词词条下的解释和例句如下：

[+ object]:to give your time or effort in order to do something or make something better—usually +in

A lot of effort wasinvested inthe project.

We need toinvestmore timeineducating our children.

She isdeeply invested inthis project [=she has given a lot of time and effort to this project and cares about it very much] and wants it to succeed.

红色字体的例句中谓语就是系表结构，不是被动语态，和你提问的句子中的invested的使用方法是一致的。