OP, you really don't have to do anything you don't want to do, end of.
And, if he's not making an effort, why should you? Although, that's a pretty bad state of affairs so early in a relationship, and you should think about what you're getting into.
But, I can't help but say, since you refer to hating the jaw ache and gagging feeling, that there are many ways to give oral without having to go, erm, all the way down, if you see what I mean. And you definitely don't have to do it long enough for your jaw to ache, fuck that. One way is to basically give a hand job, but with some oral attention on top, if you see what I mean (sorry, trying not to be too graphic
)
Not to say you should do this if you really don't want to, but if it's just certain aspects of the BJ you hate, there are other things you can try.