Dog/child
At some oftentimes unexpected juncture you’re handed a helpless bundle of joy. And into him you pour all your waking hours, love and encouragement. And you develop a unique bond that can never be broken. Until he grows much larger and stronger than you, and financially independent and then removes his own lead and moves into a new kennel with another dog who he’d rather spend his time with.
He calls you occasionally and then when you can no longer look after yourself he puts you in a home with the other old parents that you pay for out of your savings. And then you die and he gets all your stuff.