Okay, seriously...stop calling people "freaks." That's one way to make someone really self-concious. I've worked in porn shops before and the number one rule is to never, ever, call someone a freak, no matter what they are into sexually. Even if you do think it's weird, keep it to yourself.
Anyway, Batman. You aren't a freak, but I will say that your fetish is unusual and is considered strange by many people, but that does not make you a freak. If you aren't sure about how your girlfriend will react, see what she thinks of the fetish itself before you spring it on her. Ask her if she has any kind of fetishes herself, ask her what kind of fetishes she finds weird without saying anything about you liking defication yourself. If the conversation turns to defication, and she shows any kind of discomfort or disgust at all, don't try to get her to do it.
As far as the fetish itself, personally, I wouldn't do it because it is unsanitary. I'm not trying to insult you at all, but there are several ways you could get very sick or get infections from doing that. I would say you should look into other forms of sexual play and see which ones work for you other than that. Believe me, there is a seemingly endless list of things you can explore that would be much fun, and better for your health.
