Am I overreacting for feeling bad that my younger sister who’s 19 doesn’t come over now that she’s off for the summer but I know once she’s in school closer to me she will ask to sleep over when my mom can’t bring her the next morning?

No I feel this lol
I imagine there’s a lot more too it than just that too
My sister is 21 and she’s still very immature and selfish I feel like it’s pointless saying anything though as it won’t change untill she matures ( we’ve had so many convos where she ethire doesn’t see what I’m saying or says she’ll do better but doesn’t ) so it’s a live with it or cut her off situation for me
I do think because of their ages they definitely do deserve a bit of grace and time to mature though
I said I don’t think you’re overreacting because you’ve not really reacted ? You’re just a bit hurt and that’s valid

Have you invited her over? Do you guys hang out otherwise. It feels a bit extreme to feel used by her trying to be responsible and make sure she can get to school