you need to break this down to work out what the cause of your issue is.
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Is it that you dont like him masturbating?
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Is it that you want him to feel he can ask you to wank him off while you're unable to have sex
3)Is it your feelings of being a failure (and why do you feel like that?)
4)Is it that you don't like porn?
IF 4 is the issue, you need to have a discussion, you are allowed to set yourself a boundary of 'i wont date someone who watches porn' and tell him that is how you feel, and allow HIM to make the decision of giving up porn or not.
If its 1, see previous answer, replace Porn with masturbate.
If its 2, have a conversation and let him know just because you don't want sex, you still want to be sexual with him, and for him to give you the chance to have sexy fun times even if its one sided and just for his pleasure (unless seeing him enjoy himself does things for you of course, in which case, its fun for both of you)
If its 3, you need to address that yourself.
Ultimately, you can't tell him what he can/cannot do with his own body, you can tell him what your boundaries are, and he can meet you by agreeing to change his behaviour, or choose not to... in which case one of you has to have the guts to break it off.