Kill My Love (Xini)

Ten years ago, the beta was at his peak as a hit-man, when he was seriously injured while trying to save an alpha child. Having lost his edge as a killer, he retired to the countryside with a new identity to start a new life. Until an unexpected visitor showed up one day. That boy he saved has grownup to become the leader of his own gang, and now he's come looking for him with crazed intentions.

(Source: Kuaikan, translated)