You shouldn't need permission from anyone about whether or not you can satisfy your bodies needs. Did he promise you that he's not going to be masturbating? and if he didn't, why are you the one who has to repress thier sexual identity?
I think that repressing things like this only cause damage, it might not seem like a problem now, but if you continue letting him dictate your body and personal sex life it could really turn into a problem. I had a problem similar to this before, but with my ex-boyfriend it wasn't a deal of religion. He was so parinoid and possessive that he didnt' even want me touching my own body.
Anyways, so I think that you should satisfy yourself, but I don't think that you should keep it a secret from him. Why? Well, you shouldn't feel like you have to, actually. And if you keep it a secret then you might feel like you have to be keeping secrets about other things that you really don't need to. Sex is a part of life, it's needed to populate the planet, and physical intimacy is something that I think plays a huge roll in a couple's relationship. I think that you should talk to him and adress the problem, because it soiunds like it's something that needs to be discussed. Not talking about it could cause all sorts of things to go wrong in a relationship. So just approach it like an adult, and hope he understands.
No woman should feel like they need to hide themselves and repress their sexual identity. Do it to your hearts content, and I hope that everything works out for you :)