Should I Cheat on My Girlfriend?

Im mike and im 19 years old living in newyork. I met my girlfriend adrian in high school and i love her so much. we have been going out for 2 years now and i lost my virginity to her and i feel like we are going to get married. She is great i love her and she is fun and we have nothing lacking in our sex lives, the only problem is that I haven't had sex with any other girl yet and the opportunity has risen with a girl who wants to have sex. should i have sex with another girl as i have been dieing to do or should i take the chance of only having sex with one girl for the rest of my life? If i do will the guilt of cheating on my girlfriend not be worth it?