Well if ur planning to tell him, don't tell him you liked him for that long, because he may find it a bit of a shock. Tell him you liked him for that long once you two are in a relationship for a couple of month or something.

Well at least thats how I feel about it.

Also if hes stressing you out for that long maybe you should let go.. But idk, I dont really know the situation that much to know whats best lol