To answer the original post, this entirely depends on the reason your partner would become quiet. I have two examples. The first was downright shocking.

My husband began speaking to me less, never initiated sexual relations (and before, I would have to be VERY blunt because just wearing something adult rated with lots of lace was not enough to get the point across.) And he was uncomfortable with cuddling, but did so if I asked him to. He didn’t want to talk about problems, just dodged them the most he could, and all of this became the worst after having kids. (Before, not tooo bad. But not good.) His reason was inexperience and not knowing how to handle problems between us at all. I was almost doing all the work, and after the divorce, he was officially diagnosed with autism. Both of us were very surprised, but it all suddenly made a lot of sense. He had been talking to his mother, and she joked that the family doctor thought he was autistic as a child, so he actually went to get checked out. Passed every symptom, and his brother is clearly mentally handicap even more so. (Love comes in all forms, yet I was shooting for medical school. Was a startling contrast of intelligence, but I did love him genuinely.)

The second, I had no idea why he would get more quiet for the longest time. He wouldn’t outright leave, he’d just get busy in his own things, or sit around staring at the wall without saying anything. I’d ask, and he’d never answer, and got anxious if I pressed. It was difficult, I didn’t understand why he was withdrawing. Later, with lots of patience and building on each other, he expressed past abuse. Confiding problems was complaining, and complaining meant pain. Strong, silent type of man a lot of the time.