It makes sense with the proper script - there's a big difference between "been" and "being"!
"I'm just a guy who's a guy being a guy when you're not around" is the whole quote you need.
"I'm just a guy" - I'm a regular person
"who's a guy" - who happens to be male, with male thoughts
"being a guy when you're not around" - and I act like a typical male, ie. look at women (in this case, internet porn), when I don't have to behave in front of you.