I dont know what to do?

Okay so I have a girlfriend and we have come to love eachother very much and it has been almost 9 months and we do absolutely everything together and we are always there for eachother and no matter what we always make things work. But its now the end of the season for my 4th year at this campground where I have become really close friends with this girl who I secretly used to like. She usually hangs out with my sister but my sister wasn't at camp this weekend, so she had more of a chance to get closer with me and hangout more. But as we continued to hangout more and more she then starte to show signs that she liked me. I also admit, I started to contemplate liking her again but all I could think of was how upset my girlfriend would be and I began to feel really bad. So today, the girl from camp admitted that she thought I was really cute and that she sort of likes me, but I have a girlfriend so she is forced to like me as just a friend. Im really not sure what to think right now. Should I tell this to my girlfriend, or pretend like this weekend never happened, because I am thinking a lot about this girl from camp... and I don't know why;(