When you end a relationship, is it best to just walk away or remain friends?

There is someone on Fluther who I have been talking to a bit recently. She has split up from her boyfriend but wants to stay friends with him. She is still very much in love with him. I don’t know what to tell her, as I have never been in that situation. Is it best to just walk away, or can being friends when still in love be a good thing?