<human>: I've been with her for 5 years and lived with her for 3. Simply put, we're not compatible. She has BPD and while I've learned all sorts of ways to cope and help her cope, and as a result we don't fight the way we used to, I'm seriously burnt out on all the little aggressions. I'm also in a difficult STEM program and the relationship interferes with my ability to keep up with school. Also, she wants to start a family young, whereas I want to finish my PhD, and I will have to move for grad school, while she's unwilling to move.

We had a conversation recently where we laid most of these things out, but it sort of came as a surprise and neither of us really had the guts to end things at that time. 

Today our lease renewal agreement came in the mail, earlier than I expected. I don't think it would be right of me to sign the lease, feeling the way I do and not expecting those feelings to change. It's due back at the end of next week - meaning I have to tell her in the next couple days. Probably this Sunday. 

I have a very strong gut feeling that this is the right thing to do but I'm terrified. I've pretty much spent my whole adult life so far with this person and it's hard to imagine them just being gone, even if we're holding each other back. I don't know how they'll react, and I don't know how I'll have the guts to say it. This is all moving so much faster than I thought it would. I'm having a hard time keeping it together today and I really need some help.

Summarize the given text in a few sentences.
<bot>: Need to break up this weekend, how do I keep it together in the meantime, and how do I work up the nerve to actually say it?