I've had two girlfriends who were able to cry completely silently. Not just a few tears, but full ugly, balling your eyes out crying, with absolutely zero noise.
The first one I knew about her past, but the second I was completely blindsided. She didn't speak about her past, but had said that other than 'occasionally arguing' with her father she's has a good enough childhood. When I saw it, it absolutely sent chills down my spine, and I immediately knew. When I later asked her about it, and mentioned that people only learn that out for quite narrow reasons, the flood gates opened I learned more about her childhood than I was ready to.