Is it ok to cry in front of your boyfriend ?

My sister is going through a rough time with her boyfriend they been together for 6 years they just recently celebrated they're anniversary he has really bad back problems they only seem to be getting worse. He's a famous rock star he thinke he doesn't need help for it. I have no idea where she met him or how but they been together for a long time they're really close to each other since he's famous she still feels embarrassed to cry in front of him she hardly ever lets him see her cry unlees if she has to. The older he gets the worse his pain is she feels bad there's not much she can do for him. It hurts her to see him this way. She wants to know if its ok to cry in front of him ? .