Fairly common though, especially in Law Enforcement/espionage fields. Fields where there is a potential death from action. Cop shooting a suspect, or accidental death.
Andrew has killed before, we know this, but so far in every book I've written, it's come from a place of defending himself, or HOT combat/heat of battle. I have never had him carry out an Termination order before, which I find is a very different beast.
Andrew is a Lawyer turned spy. West by comparison is a Veteran soldier who has had to deal with it before. Thus their two very different persepctives.
I find Andrew isn't reacting to what he did, he's reacting to Will's judgement of what he did. That's what he fears most, and we're really going to get into what makes Andrew tick over the next few chapters. I've been eagre to do a deep dive into him. We know Will's mind inside out, but Andrew has always been a bit distant from the reader. And I was asked, before writing this one, by a reader to get into what Andrew's side of things was. Why Andrew does what he does for Will, and what Andrew's psychology was all about.
It's too easy to fall into the Mary-Sue side of Andrew, he's a character that skates the edge of it at times, and I need to be very careful of the ideal of Andrew, vs the more human (and to me, more interesting) Andrew. I don't know, I just like that there's more there. He fails, has failed before. He's made huge mistakes in the relationship with Will over the years (as Will has done in return, the can be wonderfully bull headed characters to write, and when they clash wow it's fun to write)