How do you know when he is your boyfriend?

How do you know when a relationship has gone from casual to committed? I.e. when you are officially a couple? I’m afraid of asking as he told me previously he wants something serious, but doesn’t want to rush things. We’ve been seeing each other for some time now (3 months), but I still don’t know where we stand and Im afraid of intiating another “talk” as I dont want to rush him.
We’re 27 and 28 and I have the feeling what we have could turn into something serious. We’ve even jokingly discussed what our future kids would look like…