OKAY so obviously Mushroom is pretty protective of Star. She's kind of a little sister figure to him, which will probably only get worse when he eventually remembers Isabel and her deadness, sorry2say. It's not so much that he doesn't think she can get by on her own, but he knows she's optimistic to a fault and super friendly and he won't tolerate anyone potentially taking advantage of that. Also she has died a lot for this team, which pisses him off. He gets kind of nervous when he misses a game because that's a missed opportunity to keep her from getting hurt or killed again.

Basically he's a huge sucker for Star and that's probably not going to change anytime soon, so enjoy your tiny bodyguard.