Dunno what to do

Sooooo my bf n I are really close we've been through some stuff . Now we're really intimate . He goes down on me and dies everything to pleasure me . I've told him I'm not ready for sex and he agrees to wait . I'm not his first , but he's my first in terms of how intimate we are . Problem is every time he goes down on me he expects me to do it for him .. No matter how much I want to I can't . I'm scared ,nervous and I just freak out . I've told him this he keeps saying it's ok but it's visible that he's upset ...any ideas ???