Oral Sex

So my boyfriend wants to eat me out and I'm scared. I keep telling him that and he keeps telling me it's okay and it's not going to change his opinion on me, or how he feels. But I'm still scared, I have no problem giving him a blow job, I mean I'll probably be nervous when I'm about to do it. I don't know what I should do. Should I just do it anyway even though I'm really scared? Or should I tell him I'm not ready?