Pretty much anything goes with sex IF both of you want it.  If one of you does not want it, leave it alone.    I don't know your relationship.  But, it disturbs me that he says he can't trust you when you say no.  He's messing with you, and intentionally trying to guilt trip you.  This is not an issue of his trust, but his desires.  It also disturbs me that he keeps pressuring you when he knows you don't like it.    Is your sexual relationship all about him?  If so, its not on a good footing, and not giving either of you the fulfillment you could and should have.  I suggest, if he's willing, that you seek marital counseling.  Not for the particular sex act at issue, but for your relationship as a whole.  Your question is a symptom of a problem that has been there all along.  This does not mean your marriage is bad; only that it could get better with a refocusing of self on the other partner.  Good luck.