I certainly AGREE with this one!I have to warn you, no good will come of "confronting" your boyfriend about why he's with you. Obviously he wants to be with you, that should be good enough for you and you probably need to realize that your desire to question him about it stems from your insecurity. When you question him and he tells you that he is with you because he loves you, etc, you are reassured.
My advice to you in regards to your low self esteem and lack of confidence with your boyfriend and others? Fake it till you make it. Even if you feel awkward, not good enough, etc., you need to act like you feel the opposite and soon you will begin to feel the way you have been "acting".