Emotional Breakup

I was in a 5 year relationship, he was the love of my life, my first everything. I thought we would get married and be together forever. Until yesterday he told me suddenly that he was tired of the relationship and wanted to break up. I ask him if we could work though it he said he was done. I can't stop thinking about him no matter how much I try. This is the hardest thing I have ever had to deal with in my life. He is the first person I think about when I wake up and the last person I think about before I go to bed.