I [18 m] just broke up with my now ex [18 F] after dating for two years

First time coming to this thread but its 3am where I am now and I don't really know what to do.

I just broke up with my girlfriend of two years because since I have moved into my own place and started attending college I have just felt overwhelmed with life. I have been trying my best to balance everything but honestly, nothing is balanced and everything kind of just went to shit.

I just broke up with her. We got together to talk about this issues a t about midnight and it took me three hours of spare talking and a lot of silence in order to even wrap my head around what I was about to say and try and deaden myself enough inside to not feel like puking on spot.

I didnt break up with her because of girls or anything like that. I've just felt so smothered and guilty because i was so foolish and promised her so many things earlier, that I cant even hope to keep now. I have dedicated my entire last 2 years to her pretty much, helping her with her anxiety and bipolar issues and being her rock for her to lean on.

I honestly just feel like a piece of shit human being for being so selfish i guess. For wanting to focus and get my life together... I'm not sure what I'm even doing. I just needed to vent.

tl;dr I just broke up with my girlfriend of two years due to feeling guilty and smothered due to promises i made a while back that i no longer feel i can keep. I just feel like a piece of shit for wanting to stabilize me and needed to vent. Thanks.