Punctuation

I’m not the easiest guy in the world to get along with. So when our anniversary rolled around, I wanted my wife to know how much I appreciated her tolerating me for the past 20 years. I ordered flowers and told the florist to enclose a card that read, ‘Thanks for putting up with me so long.’
When my wife got the delivery, she called me at work.
“Just where do you think you going?” she asked.
“What do you mean?” I said.
She read the card aloud as the florist had written it: “Thanks for putting up with me. So long.”