People often misuse the word libido a lot when they are actually referring to desire. Desire is what spikes our libido, and it can come from a combination of, well, everything.
People may feel like when someone "isn't in the mood for sex" with us, that it has to be because of us—but I can assure you that it is rarely the case. Think back to the times when you haven't wanted to have sex. Did you have a rough day? Were you feeling sad or stressed, or overwhelmed? Or possibly even just tired and disconnected from your body? Sometimes, we need a trigger to spark that sexual flame.
Many cisgender women are triggered by responsive desire, which is when desire shows up in response to a stimulus—something perceived as sexy happens, and the body responds accordingly. A large chunk of cisgender men experience spontaneous desire, which is precisely what it sounds like—it shows up instantly, with or without stimulation... like when the wind blows.
If this difference isn't acknowledged between two people, it could seem that they have different sex drives, aka libidos, rather than having different types of desire. This ever-shifting desire is just one part of the libido equation, which actually looks more like a combo of your brain and body's instincts: what set of circumstances turns you off, and most importantly, how sensitive those "let's go" or "let's not" instincts are to the circumstances happening in and around you.
Libido deals with the frequency people want/attempt to have sex. Desire impacts how those efforts are responded to. Some people may have really sensitive sexual brakes and lose that "in the mood" feeling easier than others. Some may have less sensitive sexual accelerators but also not super sensitive brakes and just need some buildup time. Some have super-sensitive accelerators. It's all unique to each individual.
In conclusion, we humans are inherently sexual beings— that's true. But, it's highly uncommon that daily stressors won't affect our desire. No matter how much we love our partners and may want to have sex with them, our desire can be easily affected by our kids, family, jobs, needs not being met (and not knowing how to ask for them to be met), not getting enough exercise or movement, or not having enough quiet time.
Uneven desire and libido can negatively impact your relationship when you don't effectively communicate. If this is an issue for you, consider working with a Certified Sex Coach like me.