Is it normal my friend makes love to a chair?

a little while back one of my best friends died and so i took her brother in as my friend. he comes over everyday after school and goes to his room. (he lives with me because of his parents old age) So one day I went into his room to give him a present i had bought for him for his birthday and i found him fully naked, and making love to this old chair in the corner of the room. He didnt hear me and so I left. Soon i caught him again and so i checked up on him everyday to make see if this was his normal thing. And apparently it was because he would come home every day and make love to the chair, pee on it, cuss on it, suck it, ect. he even some times, which i found the mostt disturbing, hold a picture of me infront of him and masterbate, and somehow he got a picture of me fully naked. So, is this normal? or should I be worried?