When Niki is jealous his face will often go blank. Jake will respond by pulling Ni-ki away from the other member and pulling him towards himself. Or Jake will start touching him if another member is touching Ni -ki. This happens quite often. In addition to the clips in this video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-nRj1DH716aE.html when Heesung touches Ni-ki hat, Jake touches him too at 38.25 The most obvious is in this live ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-W_gGL4MkYl4.html at 22:33 Jake did not start touching Ni-ki until Sunghoon started to get very touchy with Ni-ki. As soon as Sunghoon started to play with Ni-ki' s hair, Jake could also not keep his hands off of Niki.
It's cause niki is his only baby brother considering he raised his as jake said himself niki also get jealous with hee and sunoo basically every member lol as for jake hmm idk I have seen him touchy with everyone tho so.... especially heejake.