i have spent 3 valentines days in amsterdam , 1 of which i proposed to mrs.cheese. it can be an awesome time/place to spend with a lady friend.
if you want to go all out... check out this for something to do.. you will blow her away. the captains are very nice, it is smoker friendly and you even have a bar and you can drink and smoke and check out the city all at the same time.. oh yeah and its romantic. i proposed to the mrs on one of there boats.
http://www.privateboattours.nl/
for food it really depends on what your budget is and wha type of food your looking for.. 1 that i really like and its not overly priced is called Casa Di David.. its an italian restaurant in the spui. They are authentic and out of 10 visits to this restaurant i have never been disapointed. i can assure you that you will not be disapointed.
http://www.casadidavid.com/
february can be a beautiful time in amsterdam, i have had trips where it was 10-15 and sunny the whole trip... i have had a few cold rainy days as well.
another cool restaurant is a asian fusion place called momo. its near the museum district and it is quite trendy. the atmosphere is happening and the food was outstanding. i will be hitting this place up on my next trip for sure.
http://www.momo-amsterdam.nl/
if you want some more suggestions just let me know