This sucks

I'm basically in relationship with this guy. He's a really great guy and we've been friends since we were about 12.. we're 18 now. We've always been more than friends throughout highschool and now that we're out of school things seem to be getting really serious.

I've met have of his family and everyone refers to me as his girlfriend. I spend a great amount of time with him. We act exactly like a couple. Like we do all the couple things.. but we're not actually together. I asked him tonight if we could make it official and his response was "Why? It's not like anything would change.. that would be just giving us a title" and I get that but I feel like he doesn't want to *officially* be my boyfriend because he wants to fool around with other girls. If we continue this relationship without being official he is considered single. Basically meaning he can do as he pleases... but still have me as like his girl. What should I do? I told him that I really want to actually be with him and he said "I know you do baby".. what am I supposed to say to that.. I just muted the phone and began to cry. Please give advice 😔