I'm upset at my fiance for making me leave a less than 20% tip
Why are you upset?
She should've left a higher tip
Yes, I agree with you here. Usually 20 percent is the amount for a tip. Maybe you could have left a couple more dollars secretly but you should not make a big deal out of it something that was unintentional.
I should have, she neve would've known.
Next time try to to that. It is not good to tip servers so little, they need the money.