First, I'd just like to say that the way you feel about this is completely natural and don't let anyone convince you that you don't have the right to feel disappointed. I don't know what that one person was saying about "good grief" that it's "only been 10 days"...cause I know if that were me I'd be going crazy too! If that's what works for them, all the power to them, but it almost sounds like she's jealous that her sex life is less than that. It's what feels right for the two of you which counts.
Like many others have said, finding a balance that works for both of you is a must, and there can be many contributing factors, especially any stress from work or school and finances. One thing that came to mind is age. I have no idea how old the two of you are, but men and women reach their sexual peaks at different times. For men it's in their earlier 20s and for women it's in our early 30s. Especially if you're 30-something now and were in your earlier 20s when you started dating, you're probably used to his younger sex drive which not only made you accustomed to more frequent sex back then, but now that your sex drive has peaked, you expect him to have the same libido. Or if you have a significant age gap, that could benefit you if you're a few years older than him, or could have a somewhat negative affect if he's much older than you.
Another thought is the potential of any substance use. I'm not trying to make you suspicious or worried, but even small amounts of alcohol use and/or drugs can effect this. I don't suggest jumping to any conclusions by any means, I just know from past experience that even smoking a joint now and again can reduce the frequency because it's a depressant and quite honestly...can make people lazy and just not care as much or be as interested. And while alcohol can help set the mood at times, it can also do the opposite for some people.
Also, I'd like to elaborate on another member's brief suggestion that masturbation could be a factor. If it is, consider taking some sexy photos of yourself, or making a personal XXX movie for him - either by yourself or of the two of you together. Not only is the making of the pics/film fun to do, but you can give this to him to view during his time alone. That way you're still involved in his masturbation and since he'll be thinking about you while doing it, chances are that it will make him want the real thing!
Something else to consider is the evolution of a person's desires. I think it's great that you know he likes you walking around in boyshorts, etc. but often change and the feeling that something is new is the key to keeping things spicy. Over time people usually have at least a couple minor changes in what turns them on, and sometimes people feel uncomfortable suggesting new things to their partners, especially if they're interested in unconventional and non-traditional sexual acts. Try your best to make sure you both feel free to express what it is you're into now, what you were interested in the past but no longer are, and what you might be willing to consider in the future. If you set an open ground which you agree to be totally honest about and not judge each other, chances are you'll discover at least a few new things to spice up the bedroom, and in turn make him more interested more often. Remember that this is the man you want to spend the rest of your life with, and communication is important no matter what the subject is. But when it comes to sex, you both need to do what you can to be open and honest, because if you can't be open with each other about your sex life, who can you really talk to?! (And yes, lots of us enjoy some bedroom discussion with our girlfriends, and on posts like these, but speaking with the prime subject is key!) One way that could make this simpler is to go to a sex shop together and just browse the different items. Whether you both go through the store together, or each start at a different side of the store and grab a few toys/games/movies, etc. to show each other after you've each looked around, then you can mutually show each other what you're curious to try. This can be an especially great thing to do if verbal communication isn't your strong suit.
Initiation is also important, as previously mentioned by another poster. Just like women need to feel desired, so do men. And if neither of you are natural initiators, try setting aside a weekly date night where you make the commitment to each other to have that special time set aside always as priority, when everything else has to wait. It doesn't necessarily have to be a traditional date night out, it can be as simple and fun as staying in and playing some games with a dirty twist...even if it's unexpected and you suggest making it more interesting with a sexy bet for the winner. I find this works really well because my fiance, like many men, are competitive in nature. So by placing a bet...say the winner gets some oral pleasure, hopefully this will give him added motivation, as well as more quality time just the two of you. Add a glass of wine to help shed any inhibitions and these nights have made up many of my favourite nights with the man!
I also strongly suggest you consider and discuss the different ways that people express and receive love. I haven't read the book on it, but I know that it goes into detail about the 5 different "love languages" which people relate to and affect how we show and feel love. They are: words of affirmation, quality time, receiving gifts, acts of service, and physical touch. When two people in a relationship speak different love languages, it's common for them to feel like something is missing because we all want to receive love in that way that we express it to others. It's possible that physical touch is your primary love language, while another one could be his. This could explain beyond just a primal sense how sex makes you feel loved and how you like to show your love for him, which may be making you feel disconnected and be the reason why you are reconsidering the relationship. One great thing about physical touch as your language is that it doesn't only apply to sexual touch. It can be as simple as cuddling more on the couch, holding hands, non-erotic massage (although this can also be a nice way to lead into something more), or giving an unexpected kiss as you walk by him at home. By increasing other types of physical touch this may make you feel more loved and satisfied with you relationship. Try to figure out which languages you each relate most to and figure out how you can use this knowledge to make each other feel more loved in the ways that relate to you.
Lastly, the more often people have sex, the more often they want it! Try to keep this in mind to keep your hopes up because if you're able to even just increase the frequency bit by bit, it should be on his mind more often. Personally, I find that if my fiance and are in a bit of a slump, once we make an effort to do even something little out of the ordinary, like do it in the shower instead of in bed, or even just during a different time of day than at night before we go to sleep, it rekindles things for us. After doing something slightly different, it's like we both remember how much fun it really is and suddenly we're back in the sack every day!
Sorry, I know I tend to ramble on in writing, but hopefully this helps! :)