Jasper is jealous of Leon’s relationship Kaiden (Kaiden belongs to Hinokit) during this part of the story both partners decide to take a break and slowly build back their trust and forgiveness to their relationship.
Kaiden is Leon close friend, someone who mentor and guided him in the lgbtq+ community something Leon felt isolated from because he identifies as a bisexual which Kaiden also does himself (due to biphobia). Kaiden is a good friend and mentor who never stops working. But their relationship is purely platonic
Jasper and Leon have a long distance relationship, Jasper lives in PA while Leon lives in NYC. It’s not as if Jasper doesn’t trust Leon he’s just afraid that during their break from their relationship that Leon won’t wait for him, which isn’t the case.