Jarco literally doesn't exist outside of episodes that focus on Star dealing with her feelings for Marco. If you skipped BBtBC, you wouldn't even know that Jackie was supposed to be Marco's "girlfriend" until Just Friends. He is seen briefly talking to her on the phone in the beginning of Raid the Cave, but no context is given, and that's it. He doesn't interact with her again almost the entire Starbruary, doesn't take her to Sensei's birthday or the Bounce Lounge or anywhere, for example; in one of the mid-Starbruary live chats he said that BBtBC was their only date so far, and apparently according to the final chat, his summer plans involved Star more than Jackie.
Maybe (maaaaybe) Jarco will develop more substance in Season 3, but so far it has almost none beyond making Star jealous or making her deny her crush, and Marco still spends way more time with his bestie than with someone who is supposed to be his gf.