Im(22M) leaving my girlfriend(22F) of 4 years tomorrow. How do I do it as gently as possible?

I tried my best to make it work, and I treated her as good as I could, but I just never felt it from the other side. We stopped having sex two years ago (were 22 now), she always puts me last in priority for work, school, friends, anything. She even told me in February she got tired of being around only me, and still had the nerve to be upset when I told her I wanted to split up. The fact that I started in a new field and got a promotion before she asked me about work is also part of the issue here. I?ve tried talking to her about how I feel unappreciated and unloved, and she?s agreed with me on what the problems are, yet she hasn?t changed much. She somehow still talks about marriage, kids, and our future yet she acts like it doesn?t matter if I?m here or there in the present. The feeling of resentment and neglect I?ve had has led me to feel awful about myself, and I think it?s time to go. The worst part is that I?m going to be the bad guy for taking care of my needs. I?m going to be the piece of **** who broke all his promises, not her, even though I don?t want to leave. I still love her. When I said I wanted to marry her, I meant it, but the woman from the first year of our relationship seems gone. I can tell she tries to be more affectionate, but I can?t get the feeling of rejection out of my head. It?s at the point I?m afraid to kiss her because I don?t want to feel like I?m guilting her into kissing me. In all honesty, I?d prefer to take a few months and see how we feel before fully cutting ties, so any advice on framing it that way would help too.
We get along so well on the small things, and I don?t want to date anyone else. I?m tired of feeling like I need to ask my gf to be into me. I?m going to do it in person tomorrow, and I?m honestly scared out of my mind. I know it?s for the best, but I don?t want to do this to her. I don?t want to hurt her. She asked me to hang out and I?m going to dump this on her, either as a break or breakup. How can I do this kindly? How much detail should I give her on why?
TL;DR Im going to be stepping back from my relationship tomorrow, either permanently or temporarily and want to know how to be as kind about it as I can


Source.