The is good possessive and bad possessive. I think most everyone has seen the bad kind, and I agree it shows a lack of confidence.
The good kind is when a guy is confident in himself, and has a dominant personality, and is with someone who complements him. It reminds me of the old philosophical discussion of the difference between desire from lack, and desire from fullness. I remember that's the difference between when someone desires you because they are lacking something, and when they desire you because they have so much and want to share it.
It's the same way with possessiveness. If it's out of a fear of losing you, then it is not attractive. If it's out of love and a desire to have you completely, that's a good thing.