First of all: The average male penis is generally felt to be about 6" in length with a relatively wide variation. Hope that helps to put "stuff" (as it were) into context.
Second: The term "Penis Envy" is actually derived from Sigmund Freud. It refers not to wanting a large penis (either your own or someone else's... at least not in the literal sense). During the so-called "critical period" of psychosexual development (the phallic stage), young girls realize that they do not have a penis and (supposedly) conclude that they once had one - but that it had been removed by mumsy or daddy as punishment for their (developmentally normal) sexual feelings. "Penis envy" is widely regarded by psychologists and feminists (and generally anyone with any insight into the human condition) as utter and complete nonsense.
Third: Being fascinated by men with large penises is not a disorder as long as you are not hurting yourself or someone else, violating anyone's personal rights, and still able to function in important areas of your life. If you feel ashamed about this, it may be concerning - but most Licensed Mental Health Professionals would not view this as a disorder... unless you feel it is a real problem. (It would be akin to a man coming in complaining that he is fascinated by women with large breasts or a kid being fascinated with the latest game on the Wii. In essence - is there a problem here?)
So... don't worry about "penis envy." Nobody believes in that anyhow. If you enjoy large penises - and it doesn't hurt yourself or anybody else - go ahead and enjoy large penises.
Please feel free to let me know if I can be of more assistance.