Thinking about cheating on my girlfriend?

Theres this girl I work with and even though im in a relationship I fnd myself smacking her assss and flirting with her a lot, We hooked up last year a couple times, I dunno if she knows im in a relationship though, she hasnt asked me about it haha. We flirt a lot and just jke around and shes cool to be around, however I guess the only thing stopping me from advancing with this chick is the fact that my current girl told me she loves, me I dunno I have this mentality thats like Ima cheat before she does, not saying she will im just saying that I might as well do something first before something is done to me.