I'm thinking of cheating on my girlfriend...
Why do you want to cheat on your girlfriend? Are you thinking of ending the relationship?
Yeah, she's not right for me so this is how I'm planning on ending the relationship.
I see you are not into your relationship with your girlfriend anymore, but you shouldn't cheat on her. If you think the relationship is over, break up with her before moving on.
Even if it's not over and I'm thinking of cheating on her, why should I listen to you?
Because it's not ok to hurt your girlfriend's feelings. Would you be fine if she cheated on you ? If you think she's not a right person for you just break up with her and then you'll be free to sleep with whoever you want.