I'm not going to tell him I have a date with someone else
Are you serious about this? Honesty is key in a relationship, so why do you need to lie?
Honesty will just waste my time.
No matter how harmful something would be to your partner, you should still never lie about anything, including you cheating. A relationship thrives on honesty and following through can heal your relationship. If you lie and hide things, it will hurt the relationship.
Stop assuming you know me.
I'm not assuming I know you. Lying is very unhealthy in a relationship for anyone. Don't you think they deserve a healthy and loving relationship?