It’s too soon to tell if this is going to be a serious relationship, and your boyfriend is right to call it too soon to make it official. Getting to know each other before making a commitment is a really great idea. 🙂 I know that you want this relationship to be packaged like a perfect Christmas present under the tree, but that’s not how relationships work. Sorry! 😉
It may feel like the two of you are further along than you are because you’ve known his family and they know you, but by slowing [i]the relationship[/i] down, you’ll both be on a lot more solid footing. Your past and present long term relationships with his brother and mother shouldn’t confuse you that your romantic relationship with your boyfriend is new!
It sounds like you both want different things — you want an official relationship and he wants to be more careful because he pronounces it that — so you’re both trying to subtly push the other to do what you want. 😎 Sorry, but that never works. One person doesn’t get what they want.
My advice is for you to yield on this one, and go at his pace because it’s much better for the relationship and both of you in the long run.