Hell, I'd be a complete bitch about it if I were you! Are you an adult or what? Who is this guy and where does he get off telling you how to live your life?
I wouldn't even meet with him, just call him up and tell him that your relationships and how you live your life are your business and do not concern him. Firmly let him know that he has no right nor reason to interfere and you don't owe him any explanations. Then I'd tell him that you are very happy, and appreciate that he feels protective of you, but that he has gone too far and crossed a line where he is not welcome. Then I would deliver an ultimatum: if he continues to preach at me and judge me, he's out of my life. Done and gone. And I'd be ready to back that up for real. Family doesn't get to play that game with me, no matter who they are or how close I am to them.
Stand up for yourself!