Is it okay to stay friends with someone you have a crush on but you're taken?

My best friend has been friends with this guy for a few months. She’s been in a long committed relationship but she told me that she started developing feelings for this guy. She doesn’t wanna leave her boyfriend but she said she is crushing on her friend. I told her that she needs to limit contact and hanging out…but she said that it’s normal to feel this way and it’d be hard to stop because they work together.

I think she should take her bf into consideration and not mess with fire. What do you think?