<human>: Can you give me the gist of the text in a nutshell?

I feel so heartbroken and heavy. Everything reminds me of him and I have spent so much of my life dedicating so much of myself to him, being without him is the most awful sinking feeling. It seems as if it doesn't even phase him though, I don't understand. We broke up originally because I felt like we were distant and not working out, I wanted to be friends still because I love him so much and he's my best friend. But, while looking for another place to live (we are on a lease together until December) I spoke to a girl I know who was shocked to hear that we just broke up. Apparently he had been all over her at an after party a couple weeks ago, saying that him and I were on and off. I feel so betrayed and hurt, how can someone who says they love you make you feel like such shit and not even care. I know I am young, and I have so much time, I've been told and yet that does not help to ease the pain in my chest. Even when I try not to think about it, unconscious thoughts creep into my head and tears sting my eyes and I have to remind myself to breathe. I feel broken, like a part of me is missing and I hate feeling so weak and stupid.
<bot>: He broke my heart and I don't know how to go from having him as my best friend to cutting him out of my life, especially when I see him every day.