My Friend Stole an Xbox Game from Me and Denies It?

he came over today and we were playing some nazi zombies and he starts looking through all of my games then asks if he can have my copy of halo 3 odst in a kidding manner. then later that night i could not find my halo 3 mythic disk anywhere but i could still play with my original copy of the game but i wouldnt have all the maps. so i invite him to my game and my other friend trys to play team swat which you need all the maps to play which my friend that suposedly stole the game did not have but magically had them then and he tries to make up an excuse like he got em for free on a flash drive or some bull **** and hes still denying it. its really not too big of a deal that he stole the game because i have the original copy that i can play on also but it makes me sad that one of my friends would actually steal something from me. what should i do should i just let it go or just completely shun him?

Suggestion:

lol same thing happend to me with the same disk. I invite him back other like a week after he stole and took it back. Now i dont hang with him anymore but your friend might just be f 'ing with ya. but if he doesnt give it back it a week or so. SHUNNNNNN HIM!!!!!!!