“She stayed by his side the whole time.”
Your cousin got in a car accident and didn't wake up for a few days. He has a new girlfriend who stayed at the hospital with him every day. You're talking about your cousin's girlfriend with your mother.
She stayed by his side the whole time.
When someone stays with you during a difficult situation, they are "staying by your side". For example, you might stay by someone's side:
- during a surgery
- after an accident
- during childbirth
Usually "staying by someone's side" means staying with them physically. But sometimes we talk about staying by a person's side in emotionally difficult situations.
I can't thank you enough for how you stayed by my side throughout the entire divorce process.
Talk about something that lasts for the entire length of something. For example, you can talk about what happened while you were watching a movie:
The couple behind us was talking the whole time.
Or you can talk about driving to somewhere and following a friend's car:
I was right behind you the whole time.