There are so many issues with buying a watch for someone you love because of its expected value gain over time.
Would you buy an expensive watch you don't really like the look of as a romantic present, just because it would be worth more second-hand in twenty years??
'When presented the watch:
"You must understand my dear, you are merely a way of storing assets until we can liquify them"
Later, with her friends:
"Well, I really don't like the look of it, but John says it will be worth a lot of money in the future!"
As a side remark, my girlfriend can't stand diamonds on watches and the two watches from my collection she wears the most are 41mm divers.