First of all, in response to wanting to cum together, I can definitely say that that does not make the sex as pleasurable for the man. At least in my case, the thing that turns me on more than anything else is a girl reaching orgasm, be it from me doing oral or during sex. There's nothing better than being a part of that and then finishing yourself.

Also, I understand this whole doggy-style thing. It is by far the best position for the man, but not as great for the woman. If your bf has a problem holding out from cumming, then there are a number of ways to make it last longer for you, and for him to also cum by way of doggy-style. You can have him start off w/missionary or something like that, and then if he thinks he may cum soon but doesn't want to that way, then switch positions. Just that short break when switching is enough to give him a second wind. Also, if you want him to last longer, make him let you be on top. I always enjoyed having the woman on top because although I don't find it quite as pleasurable, I gives me a breather and isn't nearly as straining on my dick in terms of cumming. Plus, I get to watch her squirm and have a great time, so its still awesome.

Also, what Ellynn said is 100% true. If he stops while your doing it, even for 30 seconds, it will increase the amount of time it takes him to cum tremendously. And then, once you're satisfied, tell him to do you doggy-style, and he can finish. If he acts like he doesn't like the idea of all this, YOU MAKE HIM DO IT ANYWAY. Once the whole thing happens once, he won't ever complain about it. Short breaks definitely help make guys last longer if they have problems with that, and if he loves to finish doggy-style, then he gets that at the end too. That way your both happy and the sex won't be as lame.