How to tell my girlfriend

I'm sure that there have been plenty of posts similar to this one on this website, but I feel so alone and scared right now.My girlfriend and I have been together for 5 years. I'm 22 and she is 21. We have lived together for just over 1 year, and we just recently signed a 12 month lease at the beginning of September.I came out as bi to her as well as publicly about 8 months ago. I've wrestled with my sexuality for years (and still continue to do so) but it's becoming clearer and clearer that I think I am gay. I don't know how to explain the years of sex with her, or how much I love her and care about if I was gay this whole time but right now I know that I can't continue on in a relationship with a woman. Whether I'm bi with a strong strong lean towards men, or completely gay, I know that I am not meant to be with a woman for the rest of my life. I think I've always known, but there are so many factors that have likely prevented me from realizing this.We share everything, we split rent, we're financially dependent on each other. We work at the same place, we have a cat, we just did a huge move that we're not even done unpacking from yet and we're both in University. I'm in my last year and she's in her second year. I see no feasible way to make this breakup logistically work.She suffers with a lot of mental illness due to an abusive past in her family and has lots of abandonment issues, which does not make this any easier.I am so scared but I can not keep lying to her. Do you think it's worth it to make it to the end of the lease? Or at least the end of the semester? I still care about her so much and we have been best friends for longer than we have dated. I feel like this will ruin her life.I'm sorry if this rambling but I am absolutely freaking out. I don't if I'm looking for advice or just to vent but I am absolutely lost.