Hey, did you know that I cheated on my new girlfriend?
Are you serious? Why on earth would you cheat on your girlfriend?
I was out at a bar and I met someone there that I really liked, so I've been seeing her regularly and my girlfriend doesn't know. Plus I don't even know if I really like my girlfriend.
If you don't want to be with someone, it is much better to break up with them than stay with them and cheat. It would be much less messy and emotional to break things off, even if your girlfriend disagrees and is unhappy about the breakup.
Yeah, but I don't want to end things with her yet.
It's not fair to your girlfriend to stay in the relationship while cheating on her. It's extremely disrespectful, and you should just break up if you don't like her very much.