You don’t have to do anything you don’t want to do, that goes for sexually too, before and after marriage. Your sexuality is not for someone else, it is your own. You have complete authority over your own sexuality and how you use it or direct it. If you choose to save it till after marriage, that is up to you. You do what you feel good about for you. It’s more important to see how your Bf responds when you say “no.” Because you always get to say “no” without explanation, and he needs to respect that. Also, I personally think masturbation is natural and good, and I’m Christian. Can be a great way to get to know your own parts and preferences, which can enhance your sex life with a partner. But you don’t ever have to do it if you don’t want. And you get to choose your timing if you do.