I'm going to lie to a friend about not being able to go with him to a place just to go with another friend
I assume you prefer your other friend more?
Not just the friend but our plans! I'm going to be able to get so many girls where we're going.
Just let your friend know you'd prefer to do something else. There's no need to lie about the way you feel.
That might be a good idea, but I just wanted him to think I'm busy...
I can get that you wanted to spare him the disappointment but as your friend he deserves to know that you would just prefer to do something else. Maybe he'll come up with something next time you would like to do more because of it. Either way you should be honest with people, especially your friends about how you feel.