My boyfriend thinks his penis is smaller now due to past cocaine abuse. is this possible?

Not possible: Perhaps under the influence of cocaine, your boyfriend had an exaggerated perception of the size of his penis. Now that he is off the drug, he has a better perception of reality.

Possibly: Chronic cocaine use alters brain's parasympathetic nervous functions that help sustain an erection during sex. The chemicals in cocaine gradually take over the brain and nervous system, causing the brain to become disoriented. The neurotransmitter nitric oxide and dilator cGMP become suppressed, leading to poor erection or orgasm dysfunction. After prolonged use it could become permanent.