What? What did I do? Did I say something?
The thing about women is that they all speak in code, just like men do. There's certain sayings and actions that are intrinsic to us, and it allows us to understand people of the same sex.
Men don't habitually open up and share their feelings with each other because it violates their code. They know that they're supposed to be proud, independent, strong men that don't lower themselves to the level of asking for advice. It would just be unnatural.
Similarly, women function in like manner. Why do you think women know so well when something is wrong? Because it's their job. Women tend to open up, share their feelings, and empathize. So, when one woman is upset and not as talkative, her friend will discern that something is up and try to talk to her about it. If she is reserved from talking about it, her friend will know how to empathize with her and persevere to make her feel as good as new.
Now, because men generally want to be left alone when something is distressing them, men feel that when women are having off days, they want to left alone also. DO NOT make the mistake of leaving a woman to tend to her feelings. Of course, she can always talk to her women friends to resolve the issue and feel better, but then, what good are you for??? You made some sort of commitment to this woman; you might as well try to care about her by trying to understand her ways. Empathize. Talk to her. If she tries to be humble and modest about her situation or says she doesn't want to talk about it, don't assume that that's how she really feels. Women often are afraid of coming off as needy to men. If she looks hurt or sad, help her!
Of course, women can hint all sorts of things when they talk. This is how women can read other women's minds. They're used to it. However, since they're dealing with a whole different species (men), they assume that men are experts at discerning feelings too. It's a bad habit, but most women don't understand that men work very differently. You might have to explain it to her if she continuously gets irritated.
Knowing this, pay careful attention to what she says so that you don't come off as stoic. You could be talking about a girl, casually, and she could get a little coy. What is she hinting? Jealousy. If you start talking about the depths of your relationship, and she starts to doubt a few aspects or even puts herself down, she is looking for reassurance. For you to confidently tell her that it will be alright and that you will be there for her.
It's a pain to have to translate women like this, but men and women each have their own unique quirks. This one's just one you'll have to accept, just as women will have to accept mens' quirks.