how to become best friends with your boyfriend ?

Just realized my boyfriend and I been together for years and barely know much about each other. I want us to have that solid connection I see in relationships and not just surface stuff. I've always been a bit shy and scared to let people in. I don't have many friends but I always felt something missing from my relationship. I've realized it's that we aren't best friends ? How do you become best friends with your other half? Is it too late to do since we've been together so long ?