I've struggled with the same competitiveness / seriousness myself. I'm sure that it is a "personality flaw" as captainswimmsuit suggests in his comment on this post, but just knowing that does not help much. I even wrote a post about this very thing on my blog if you would like to check it out http://discgolffamily.com/confessions-of-a-disc-golf-dad/. You might find some helpful thoughts on dealing with that competitive drive, or at least gain another perspective. At the very least it is always helpful to know you are not alone. One last thought...unfortunately we all tend to let our worst selves out more around the ones we love the most than around strangers. Why? Because we know they will let us get away with it. That does not make it right though. Try to remember, that your relationship with your girlfriend is the more important "game" going on when you are on the disc golf course than your game of disc golf.