As of the final season, he gains a love interest in the form of Ashi, an assasin that was born to originally kill him but realized the error of her ways. It's later revealed that Ashi is the biological daughter of Aku which forces her to unwillingly attack him due to Aku's influence. However in the final episode Jack and Ashi's love for each other gives her control over Aku's powers sending the two in time to kill Aku for good. Sadly before Ashi and Jack are married, Ashi is erased from existance because Aku's death altered the timeline.
In his mourning, Jack sees a ladybug on his finger and remembers the good times he shared with her forming a smile. Also in Chinese mythology, when a ladybug comes to call, true love will visit and the spots represent the months until she appears, hinting that Jack will find love again.