Hey there, Melamyl.
You might be comforted to know that this is one of the most common sexual dynamics for all couples. Because desire for sex for all of us can be so conditional, ever-changing and also so unpredictable, it's very common for this not to line up with most people or, if it does, not to stay lined up. The longer we're in a sexual relationship, too, the more likely it is that we'll deal with this, and probably far more than just once.
The good news is that we do not HAVE to have our libidos "match." We can make our sexual relationships work for everyone even when they don't, and certainly without the person who is feeling less desire trying to make themselves have it more. Masturbation is usually one of the main answers to that, as can be other kinds of intimacy.
In other words, if the person with more frequent desire is mostly just after the physical aspects of sex, masturbation usually answers that just fine so long as that person is given privacy, time, space and support for masturbation. If they also, or instead, are mostly looking for the intimacy sex can provide, there are many more ways that sex to share intimacy with a partner, and some of those ways may be things that you *do* also have the desire for.
Let's start with all of that: how does that all land with you?
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead