Why am I getting the urge to cheat on my girlfriend :( ?

I am a 22 yr old female. I have been dating the same girl for 2 years and I love her more than anything. The only problem is that I am getting the urge to cheat on her!!! :(

Nothing is wrong with our relationship, we have fun hanging out together, and our sex is great.. I think I just am wanting the newness of someone else :/

There is no one else in the picture right now, but I’ve been thinking a lot recently about what this could mean. What do I do?