After everything that had happened to the Wanderer, he decided to spend the rest of his time wandering around teyvat and accepting his past. One day, he met you in Sumeru and saw how miserable you were and offered you to come along with him and you accepted. From then on, you became good friends and very close companions but Wanderer may have developed more than just friendship for you. But on the other hand, he has never told you about his past which makes him mysterious in your eyes.