[Jack is most certainly not the kind of person to judge who should be together, and he’s definitely seen much, much stranger couples in his time!
Given that he likes both of them and doesn’t want to cause trouble in what is presumably a monogamous relationship, he keeps the kiss light – but lingers long enough to demonstrate his clear enjoyment of it. He also moans softly at those hands on his chest, because he always loves touch, of any kind!]