To wish to escape from solitude is cowardice. Friendship is not to be sought, not to be dreamed, not to be desired; it is to be exercised (it is a virtue).
There is no good way to say "I want to be alone" because the person I say it to assumes it is out of sadness and therapizes it or immediately feels insulted and becomes forcefully annoying out of insecurity when all I want to do is engage in my mundane habits without commentary.