There’s a moment in The HitchHiker’s Guide to the Galaxy when Slatribartfast asks Arthur, ‘Is that your robot?’
‘No,’ says Marvin, ‘I’m mine.’
This scene comes to mind every time I hear a barbershop tag that finishes a love song with the information that the beloved is now, ‘Mine, all mine’. However much sympathy I have had for the sentiments expressed up to that point (which is often quite a lot; I’m a soppy old soul despite my misanthropic appearance), it largely evaporates in the face of this blatant possessiveness.
You can’t own the person you love most in the world. Even once they have decided to team up with you so you can build a life together, they are still their own person with their own preferences and opinions and needs and – most importantly – the right to determine their own destiny. Asserting that they are all yours doesn’t make you sound romantic, it makes you sound like Monty Burns gloating over a pile of gold.