How to survive a break up?

I’m in the beginning stages of a break up currently. My boyfriend told me he wanted a break, but I know it’s only a matter of time before we fully cut it off. He is my absolute best friend. I tell him everything and see him nearly everyday. Things just changed. I love him so much, and he says he loves me. However, not everything is meant to work out. He and I have been together for nearly three years. We’re super young. We got together at 15, and are now 18. We grew together, and I haven’t known a me without him since I was younger. It’s terrifying the idea of letting him go. I love him so much, and have no idea how to do this. I’ve never been through a break up before and i’m just hurting so much.