HELP!! Advice!?

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I've been with my boyfriend for a year now. I am 16 and he is 15. He wants me to give him head. I've done it before but I don't want to anymore. It's so disgusting and it makes me want to puke. He keeps telling me he wants it and keep saying no. I've told him that in past relationships that I've been left because I didn't give them what they wanted or I didn't give them what they "needed". And I feel like if I don't donut he'll eventually leave me and find someone else who will do all of the things he wants. We are both virgins and it's staying that way until marriage. I just need to know if I'm being pressured and what should I tell him next time he ask and I say no.