I don't normally post without reading the thread, but I'm going to on this occasion as I'm finding this quite distressing to read. (Got as far as p3.)
OP, If you're not sure, don't do it. The fact that you started the thread confirms that you're not sure. If you liked the idea, you'd have known straight away. He keeps on coming back to the same thing after you've said no? That is pressure. If you give in, what will he want next? You'd be opening the floodgates, he'd know that all he has to do is keep on "gently coming back" to it and you'll give in.
I've had some bad relationships in the past, and too many times I've done things sexually that I wasn't comfortable with, and you know what? I felt like shit afterwards. Miserable, disgusted, and ashamed of myself. Just do yourself a favour, and don't put yourself in that position.
I'm not passing judgements on anybody else's preferences, if you're happy with it, go nuts.
Apologies if what I've said has already been covered. Will see about reading the rest but no promises.