Choices and Losses

Unable to deal with loss. Friend and I said goodbye today. He's moving in with his love. As much as I want him to be happy and she makes him so, it's killing me knowing I'll never see him or talk to him again. I don't know how I'm going to live without him in my life. I've been unable to move forward after losing R; how can I open up again when doing so caused me so much pain? How do I sift through the thoughts and feelings and find the ones that will comfort me when I'm grieving, keep me sane when I feel as though I'll go mad with loss, and feel loved when I'm alone? If I knew why, maybe it would help.