Compulsive thinking..about my fiances past? help!?

I am always bombarding him with questions about his past and what the girls were like and the positions and its not jealousy. its compulsive thought processes. i try to let it go for so long and it keeps bubbling until i explode...and have to ask. i just need some advice please! i just always think about him with other woman. i have never loved anyone or have been more happy IN MY LIFE. this is the man i want to marry so why is this happening?