As much as I care about my girlfriend, I send her flowers at work to remind her coworkers as much if not more than her to say "hey - she's mine, and I love her too!". She's very attractive and works with a lot competitive guys that ask her out all time, so they back off and she feels loved
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And, she's not at the age yet where she thinks about opportunity/differential costs with what I spend my money on, so I'm toast if I try to explain that are better things to spend money on than flowers!