So it's, in my opinion, a better way to say: "you mean the world to me" because the universe is infinitely greater, bigger, and stronger than just the world. "And a half" is the basic meaning of it, where in this case, you'd use it as a way to say that something is very good, large, etc. ( in a positive sense, of course).
"You mean a universe and a half to me"
by Prince of death January 9, 2023