if that was the aim of the show, or one of the messages they wanted to convey, i doubt they would have made Star actually start developping feelings for Marco. and it's not even a one-time thing, throughout season 2 they've been dropping hints that she at some point started feeling more than just friendship.
and it's important to note the contrast between this and season 1 where they really were just buddies going on adventures and she'd hug marco without a second thought, or would even try to help him get with Jackie.
as it is now, either things are gonna go south with Jackie at some point (or she'll move out of the picture for some reason), or Star is just gonna have to get over it and move forward despite her feelings.
but the possibilities are endless right now, ranging from Jarco remaining until the end to the situation reversing and Marco becoming jealous of Star after she finds some guy like Oscar to hang out with and things going from there.
we still have a long way to go with 8 episodes in S2, the whole S3 and possibly more seasons after that.