Maybe he's getting negative signals from you regarding sex? Are you really passive, or non-communicative about sex? He will take that as a "no I'm not interested" signal. Clear communication is important. How about if, when he goes to the bathroom for a wank, you knock on the door and ask in a friendly voice "Can I help with something?" or "Can I have some?"
The other thing I have to ask about is sensitive, so try not to get defensive. Is he physically attracted to you? Are you overweight? Most guys are not into heavy chicks. You need to be honest, are you truly overweight or just a little soft? Because physical attraction MIGHT be an issue here.
The other thing is, how often does he have a wank? He might be addicted to porn. Cut off the porn, and see if his attitude changes. Talk to him and tell him the porn might be affecting your relationship, so you want to stop it for 3 weeks. If he can't talk about issues, you two won't be able to sustain a long-term relationship.
I have a long time interest in psychology, specializing in relationship dynamics for 30 years.
(Please note, we give the best advice we can based on the information given in a post. For better advice, please include the age of all romantic partners.)