could it be her ? the way she smells down there...moans...moves...expression on her face...to your standard, is she hygienic...bad breath...dirty finger nails...smelly feet...
all a.m. could easily ruin the mood.
otherwise, I can't think of anything else that cause lost of sex-drive at age of 23 (alcohol is bad, but at this age, it won't matter much..been there)