Getting tired of my GF Hypocrisy

Hi Everyone,

So I've been with my girlfriend for 2 years now. She had and still kind of has this really toxic habit where if I don't reply to her messages within even 8 minutes she would raise hell and get really upset with me saying things like "if you don't want to talk to me just say so" or some bullshit like I don't love her or something. I try to reply as soon as I can but I get busy with work, or I don't always have my phone on me or studying which she knows. She would give me so much shit about it. For me personally, I understand people have lives so I don't care if someone gets back to me a couple hours days or weeks or what not. She however, is really starting to piss me off. Even during those times and even now she leaves me on read with the read receipt on and doesn't say anything until an hour or so later. She just says "omg i didn't see this" like everytime. Just now, she went out to get dinner with her friend, was messaging me then left me on read again. Like I have mentioned before, that is totally fine but what gets to me is that she gives me a very hard time when i do it, even though i can't always reply on time as I get very busy with work and even tell her that. What are your thoughts?

TL;DR - GF mad at me if I dont reply to her messages quickly even if im super busy but she doesnt always reply to me and leaves me on read with read receipt