I'm planning to lie to Harry.
Okay....why do you want to lie to Harry?
I'm planning to tell him that I like him.
If you don't like someone, you shouldn't lie to them. The lie will only grow and become a burden overtime and you will regret having told the lie in the first place.
I have to lie since I don't want to hurt him.
It may feel easier right now to lie to him to spare his feelings but he will be even more hurt when he finds out the truth. Its always best to be up front and honest even if it feels more difficult at the time.