Reason: Joe wanted to run a way and start a life with Marienne and Henry, but Love would never allow that.
Method: Aconite injection
The icon, the legend, Love Quinn. Joe's wife might have been a ~tad~ impulsive, but she was his equal in every way. Things were only ever going to end badly between this pair of obsessive serial killers, but there's a part of all of us that wanted her to make it out of Madre Linda instead of Joe. It wasn't the most graphic of Joe's kills, so what really makes it upsetting was Joe's cold, self-righteous attitude about the whole thing.