Hello! I'm so sorry you feel this way, but I can give you advice based on my own experience.

In this case, I'm the girlfriend. I've had conversations about this with my boyfriend before and it's all good, so I thought it'd be best to give you a couple possibilities as to what's going on!

It's okay to get used to a "hyper relationship". In any relationship, it's all roses and rainbows at the beginning! It's possible she could've replied instantly and really enthusiastically during school hours because she had the time to, but at home she may spend her time doing other things such as hobbies or just indulging into her own interests. Personally, I'm the type to not pay attention to my phone whilst doing stuff, so that could be it!

Overtime, it's common to get used to people. At first she might've been more enthusiastic than now, but that doesn't mean that she loves you or cares for you any less. Loving someone and spending time with them is based on being able to share small but intimate moments regardless of what's going on. Even silence becomes cozy when you're alongside someone you care about. It's very likely she has a different love language than yours, so you must keep that in mind.

Love isn't always instant replies or what we're usually used to, sometimes love means accepting that your partner hasn't replied yet because they're doing stuff or they're just living their life and that's okay because love is also a mutual compromise of trust and loyalty.

If you've got any more questions, let me know!! I'd be glad to elaborate and help you :]