She's a spy pursuing her own objectives, she can't just ditch all that to get together with Leon. The less personal attachments she has, the less likely someone would try to use them against her. She definitely cares about him, a lot of her storyline is about her wanting to be together with Leon, but the image she is struggling to keep is that of a cold, independent and stoic woman whose strength lies in her ability to be incredibly calculating ad strategical. To show her feelings would be admitting her weakness, which she did in 2, got slammed into a monitor by a tyrant and almost died as a result.
As for if she knew...Probably not, but it doesn't really matter. There is no such thing as bodily harm amongst protagonists, Leon took giant bone projectiles to the back and was perfectly fine.