Marco loves adventures, and Star is his main source.
Marco really enjoy their friendship, watching movies and shiet.
Marco prioritizes Star over anyone.
Marco always support Star, even if sometimes she is wrong, and Star not always can do everything for her own.
Marco just wanted a quiet life, having fun with Star while having a crush on the sk8er girl, nothing more, but plot demands him to be pathetic, he still needs to grow up, we still have one season and a half.