I hate my gf - idk how to breakup

I used to be head over heels for her, I loved everything about her and thought that we could spend our lives together. We've been together for 4 years, since we were 17. I knew her 2 years before as well. We're the same age.
Over the past year and a half or so, her behavior has been all over the place. Sometimes she says she wants space, other times she says that I'm acting distant. We go to different unis, only 2 hours by drive apart so its not a hassle to meet up but it seems like theres almost an argument every time we meet and i just miss the way it used to be. We often facetime and when she gets ready, she shows me what shes wearing and asks me for my opinion. There are some things she says which make me worried, sad or angered because she talks how her ex was more protective over her and the things she would wear but when i used to be like this, she would always tell me that I'm controlling and that made her friends hate me. Anything i do or say, she will just make something bad out of it.
I thinks she's already cheated on me like 4 months ago because one of my mates literally sent me a video of her acting with a guy so I've lost feelings along time ago. I've been working on myself, building muscle. The reason I haven't broken up with her is because i know she'll make a massive scene, whether its in public or online. We've been close to a breakup before and she posted everywhere on Instagram how she was broken beyond compared and her friends started to attack me and my friend were drifting apart because she made up a rumor that i cheated on her so i don't want that to happen again.

I think we're just not compatible anymore and she has to turn everything into an argument. I've tried helping her and talking things out but she just says its one of those days but it just seems to be everyday. Its my first relationship so idk how to play the break up game especially when she's a bad person. I don't want to stoop to her level and be a bad person myself but idk what the best plan to go abt this is

I've never been in a "real" relationship and out of curiosity how did you not see any of these signs in the first 3 years of being togeather? To me it does sound like shes been seeing other people based on her behaviour and comments but im just speculating. Any friend who drifts apart from you based on a rumor wasnt really a friend in the first place imo...

In all honesty, go talk to her about it - it's the best thing to do in this situation.
My best advice it to explain your honest feelings towards her and how her behaviour has affected you throughout these years.
Don't be scared to break things off with her; from my perspective when reading this - it seems as if she's quite insensitive and careless (as in she doesn't put much thought into holding the relationship together). You definitely deserve better - I'm not saying she's a bad person, as she might have her own issues and problems she's facing; however, this feels like psychological abuse and damage to a person's own well-being.
I wish you all the best and hope things go well both ways.
Goodluck and do whatever makes you feel comfortable!

yeah thank you imma figure something out thank you