He should definately not be demanding you to it if you don't want to. Making love should be something that comes naturally between two people who are in love, therefore if he does love you he shouldn't be demanding you to do it and no matter how much it hurts that you keep refusing to do it, he should be keeping your feelings at heart.
But like what many people have said on here - If he gives it to you, you should give it to him. You can't expect to take without giving it back.
And what he said about marriage is Bull - does he even know what marriage is about. Obviously marriage doesn't consist of giving oral all the time. It's about love and officially joining 2 people together.
a few days ago, i was discussing witha few friends about the problem people have with giving oral sex. I agrued that giving oral is a sexual act which doesn't haven't to be given but can be if you want to. A friend, a male, said he couldn't stand the fact that people give orals becuse he finds that it is an unclean method of sex and the thought of kissing the same person after is revolting.
Although, giving it may not be pleasuring you in any way - (like others have said) wouldn't pleasuring the person you love be pleasuring you? But in your situation, he doesn't deserve any pleasure if he can't respect your feelings. Make the right decision - don't let him pressure you into anything!!!!