people have stated the obvious here, but yeah its fake. there's no way they happened to find a handsome actor with a big penis (because again, they weren't even checking for that) to perfectly fit the role, and even moreso, be able to play a part in the "love rival is bigger and better than me" physically for this scene. and at no other point do we see it, despite seeing him from numerous other angles where it would be obvious he hung that low.
its also very weird the defenses yall come up with to hang on to these fantasies. the reason any even cares is because penis on tv/movies is like shocking. it was just a huge deal cause the UK had its first erection on tv recently. idk why yall think mainstream tv is just gonna slap a real 10 incher in there all of a sudden