That you are so insecure is what is broken. You can never become secure by trying to control outside people/situations because you do not have control of them, ever! He can tell you until he's blue in the face that he's not looking at other women and will you believe him? No. Too, he may be looking and you can't know that.

Work on your insecurities; not in terms of caring/not caring if he looks but on knowing you're the finest/only you out there and that you know you and him and that you know he can look but he ain't gonna want anything other than you and/or if he ever does, that's him, not you/your fault and you can deal with that if it were to happen.