So i like my really good friend and i want to tell him but i cant cause it will ruin it what do i do ?
Don't project your feelings on him. Accept the reality of situations. That said, be brave by being honest, anything is possible, and all things do change. Tell him what's on your mind.
what do you really have to tell him?
You can do little things that give hints on how you feel about him. However, you should not be too direct because it might push him away if he is not ready to change the status of your friendship.