There is a similar post to this here: http://boards.weddingbee.com/topic/sexless-relationships
To answer your questions, while we are not on a dry spell per se, we do go through them. And we don’t do it as much as we’d like, so maybe that is a dry spell? Like you, we have been together a long time (5 years) and sometimes it gets a bit repetitive. We had a great 4 years where we much more often desired to play twister, but I recenly started a new pill that has greatly decreased my drive, and also started grad school for my doctorate, which leaves me stressed a lot of the time. Hence, we sometimes go through periods where we aren’t intimate for longer than we’d like to admit, and like you, I sometimes feel like I could be totally fine going for quite some time beyond that, while he is eager to break the streak. They say that the less sex you have, the less you want it, and vice versa, and I do think that is true. We also don’t live together, though he has his own house and I have an apt, but like you, when we see each other we often feel like we "have" to, which sometimes interferes because, well, that’s not a fun way to get in the mood! Also, we sometimes only have a few hours together, and we’re so busy that we simply don’t have time.
What keeps me from worrying is that I know we’re still very attracted to each other, and would (will!) definitely do it more often if we lived together and had more time together each week. Also, I know my body, and I KNOW that this new pill changed things for me hormonally. I don’t plan on staying on it for too long into our marriage.
Like you, my fiance doesn’t get upset when I don’t feel like it. He voices that he’s bummed, but he understands. And sometimes, he even admits he’s too tired. Sometimes I wish I had the kind of FI who would never take no for an answer (bc he wanted me THAT bad!) but I’ve learned to look at the bright side- that I would never have to be totally talked into it. I’ve been in that kind of relationship and it sucks. If you are worried about him straying, have a serious talk about it with him. Also, I’d recommend seeing a doctor to see if it’s something medical. It sounds like you’re bummed about your body and that has a definite emotional effect on sex drive.. as does being overweight, if that is a problem for you.
If this is the only thing in your relationship you are concerned about, just talk to him and your doctor, and I’m sure you’ll be fine. Are you still attracted to him? When you do have sex, do you enjoy it? Are you concerned about what it means for your relationship, or are you just worried that if he doesn’t play twister enough with you, he’ll start playing with someone else? I think the answers to those questions are pretty important for you.