boundaries - oral sex

My boyfriend has recently taken an interest in becoming more 'experimental' - he has always spoken about oral sex and how much he desires it. I have never done it nor have the urge to. I feel obliged to try but I can pull myself to enjoy it nor endure it. I have a mental block on him going down on me. The more we talk about it the more he wants to. What do I do? I want to please him as well as enjoy it myself - what are my options?