3C

Was Kat right that it was better for them not to get involved with someone?

Yes because under extremely stressful situations as their jobs put them under it's best not to be personally involved with those you work with.

In their line of work personal involvements could be a distraction that could be deadly.

I think it would be easy for some bad guys to kidnap or kill your loved ones in some sort of revenge plot. We've seen it as a plot driver in numerous books and movies.

It could skew your judgement if you have an emotional attachment to somebody who then gets captured.
Best to keep a clear head (if you can: Gray and Rachel seem smitten, however).

I suppose it's easier if it's not someone that you are working with where they could be used as leverage. But, that said, how many times in our books have we seen families and friends not involved in the current action (The Hit? The Sixth Man?) being threatened to ensure someone's cooperation. so unless, the operative is ready to live a solitary life, I think they need to connect where and when they can.