>>89599942The thing is that she didn't realise she has romantic feelings for Marco. She probably still hasn't really realised it.
That's the point of the recent development for her; it's the experience of only realising you actually want something when it's gone and only awakening to having romantic feelings for someone when you see them getting romantic for someone else. It's quite human, and as Star is only just soon turning 15 she's probably never experienced that before, the slow transition from liking someone as friends to having romantic feelings for them.
So until now, she hasn't had romantic feelings for Marco, it's been friendship, and she's genuinely wanted to be a good friend and see Marco happy with his crush, Jackie. The romantic attachment has been growing so sneakily she hasn't realised it herself, and has thought that her intensifying feelings for Marco are still just friendship.
It's only when she actually experiences Marco leaving her side and going off to spend romantic time with someone else, sees him give loving looks to another girl - and the other girl return them, sees him slipping away from their special bubble and forming a meaningful relationship with another girl when she suddenly feels that she doesn't want this after all.
But I think she still hasn't realised she feels bad about Marco not being at her beck and call and getting intimate with Jackie because she's crushing on Marco herself. She just doesn't like it but doesn't realise why - and she'll still keep on a conscious level holding on to the old dynamic of being a good friend who supports Marco in his quest to win Jackie's heart, while subconsciously wanting Marco to stay with her, wanting their special bond to be the most special relationship Marco has, wanting to be the most important girl in Marco's life. Which will create conflict.
