What does "onions have no hearts" mean?

The onion has no heart is a metaphor for some Chen Shimei: \x0d\1. Onions do not have an obvious heart like Chinese cabbage. \x0d\2. I will cry when peeling an onion, but I will insist on peeling it to the end. \x0d\3. When I finished peeling it off with tears streaming down my face, I realized that it had no heart at all. \x0d\4. It is a metaphor for some infatuated women who sacrifice everything for the men they love, but in the end are heartbroken by ruthless, meaningless men.