He definitely had some issues as well. For sex he let assassinating informants and others (non-militant?) slide. It seemed like he still tried to keep the sexual relationship going even after she told him she did some side work cutting a body into pieces, though it was harder and eventually led to him moving on. All around no bueno.
Nobody is the villain of their own story.
THIS!
I'm sure that she's the victim in her own story.
I suspect living in a war zone does this to people, which is how he explained it. Somehow he was able to see his girlfriend as a soldier instead of a murderer when the two were conflated.
Rationality is not what humans are best in. People stay in toxic relationships, or make babies in the middle of a war.
We are driven by chemistry much more than rationality.