This may mean that your boyfriend needs some personal time and space to concentrate on his studies. He doesn't want to be disturbed from Monday to Friday in order to finish his study task better. This doesn't necessarily mean that he doesn't like you, but he needs some time to concentrate on his work and hobbies. As for the portrait of a couple, maybe he just wants to keep some private space. You can talk to him about your feelings, understand his thoughts, and find a balance point, so that both of you feel comfortable and satisfied.