How close are you and your friend Tj? Does he really know you that well? If not, then he's probably just saying that because he wants you as his.
The most I can tell you, is FOLLOW your heart. If Matt has been there for you through everything, and he's your best friend, and you truly love him, then I would just give him time to adapt to being a boyfriend. Not everyone can go through a relationship at a fast pace, and honestly, I think it should be taken slowly anyway.
I know for a fact that when your boyfriend is your best friend, the relationship is usually pretty good

Cuz you know each other as friends. And that's the best way to the start of a relationship.