The reason for doing it next weekend is because Sunday is our only day off work together, and I have a huge exam on Thursday and Friday. Sunday is our only chance to talk in person. 
For some context, I (25afab NB) have broken up with him (32m) twice before and we’ve always found our way back to each other. The second time I broke up, we never officially got back together, we just kind of drifted towards each other again, started sleeping with each other and I started living with him again. This was a little less than a year ago.
A month and a half ago I started living at my place again, meeting old friends and new people, and it’s made me realize I want to try polyamory. 
I know from bringing up in the past that this is a dealbreaker for him, but I want to choose my happiness this time over, not his. Problem is, I feel so so horrible since reaching this conclusion I know that this is the right long-term solution for the both of us, but I still feel like shit. I’m anxious, have trouble sleeping, and my stomach is turning all day. I want to wait a week so we both have the opportunity to talk, but I don’t know how I’ll make it to then. I wish I could just disappear and stop existing so these horrible feelings will go away. How do I navigate this? I need help. 

TLDR: I want to break up with my partner next week but I feel so fucking horrible I and I don’t know how to cope