Saying "The only major problem we seem to have is how often to have sex" is like saying "The only major problem with the stock market is how much lower it is." This isn't trivial.
You're right, sex isn't everything. At this early stage of your relationship--and yes, in the grand scheme of things, it's still early--it's a warning bell, no, make that a warning "gong," that something is very, very off. You need to address it. Immediately.
The first thing you should know: this isn't normal. Unless you're 18 and your fiancée is 73--hey, we're not gonna judge--this isn't about gender differences. You have a healthy sex drive; most women have a healthy sex drive...unless there's some other issue, usually psychological, getting in the way.
There are many such possible issues. She could be depressed. She could be having second thoughts about you. (No kid gloves here, sorry.) She could be super-super pissed about having to plan the wedding herself, and she's just lost her sexual appetite. She could be nervous as shit about your decision to get married, and her body betrays what she's afraid to discuss. She could be somehow aware of your wandering eye (chicken or the egg?), and feeling less sexy because of it. It could be any or all of these factors.
Something else you should know... in all likelihood, you're unwittingly making the problem even worse. Great news, we know. With your "off the chart" sex drive, every time you attempt your seduction--which, hopefully, involves a little more foreplay, humor, and tenderness than just pawing her as she drifts to sleep--you make her even more self-conscious, anxious, and feeling even less sexy. It's a vicious cycle: less sex leads to less sex. Back to the stock market analogy, it's just like how unemployment leads to more unemployment. But here's where the analogy breaks down: over a long enough timeframe, the economy moves in cycles--recession, recovery, boom, bust. Unless you dramatically change your dynamic, we're not predicting many booms, and the only "busts" you'll be seeing are the waitresses, neighbors, and co-workers...the "other women" you mention, as you're already sniffing the road to infidelity.
So. Here's what you need to do.
Talk to her. Have a good, lengthy, relaxed, no-pressure talk. Don't get upset. Don't whine about the drought. Don't put her on the defensive. Instead, ask her if she's happy with your current amount of sex. Ask her if there are any other issues that you guys should work through together, as a couple. Tell her that you love her, that you want to be with her, and that you want to work-as a team-to figure out why you're not connecting in the bedroom.
If you're really, really lucky, maybe this conversation will unlock some hidden issues and you can move forward. More likely? It won't be a panacea, and, I'm sorry to say, you should seek the two least-sexy words in the English language: couple counseling.
Yep. It's that serious. Remember, you're about to decide the next 50+ years of your life. Don't sweep this issue under the rug. Don't lie to yourself and hope that "things will be great!" once you've kissed the bride. Marriage isn't a cure for a broken relationship. That's what babies are for.
Think about whether she's right for you, whether you're right for her. Talk to her. Then talk to a professional. It's entirely possible that she has cold feet. And, given your wandering eye, it's entirely possible that you're not convinced that she's The One, in which case you should explore that decision now, not after marriage. And it's entirely possible that she's fine, you're fine, but she's just overwhelmed by her tyrannical boss. You won't know until you ask.
Good luck. Please let us know the resolution or if you have any follow-up questions.