There are people I don't get on with, but they're important to people who are important to me so that means I have to make an effort.
If they get hurt or killed, that upsets the person who is important to me, ergo I am upset.
Jeb was important to Devon, Jeb was killed, in Alvarez's house. Devon, who is important to Alvarez, was hurt as a result. Ergo Alvarez is going to go an avenge him. Because that, sometimes, is the messy reality of love. Alvarez feels guilty, shamed, and angry and vengeful and protective. It could just have easilly been Devon, had Ephraim managed to get Devon alone instead of Jeb. It still might, Alvarez must put him down. The law won't do it.