(AS BASED ON MUFTIS' ADVICE)
If a husband gives his wife flowers on this day to express his love, he should ask himself:
"Why did I choose this one day for expressing love termed as “valentine's day” and not any other of the 365days? Why did I decide to express it on the very day every other Christian and kafir celebrates by doing similar acts of giving flowers? etc.
In Islam we should express our love everyday and not just in one particular day in which non-Muslims specify for expressing love. Here is a piece of information on the history of Valentine's Day written by those who celebrate it.
The Kuffar write:
Every February we celebrate Valentine's Day by giving flowers, candy and cards to those we love. We do this in honour of Saint Valentine. You may be wondering, "Who is Saint Valentine"? Legend has it that Valentine was a priest who served during third century Rome. There was an Emperor at that time by the name of Claudius II. Emperor Claudius II decided that single men made better soldiers than those that were married. With this thought in mind he outlawed marriage for young men in hopes of building a stronger military base. Supposedly, Valentine, decided this decree just wasn't fair and chose to marry young couples secretly. When Emperor Claudius II found out about Valentine's actions he had him put to death. Another legend has it that Valentine was an imprisoned man who fell in love with his jailor's daughter. Before he was put to death he sent the first 'valentine' himself when he wrote her a letter and signed it 'Your Valentine', words still used on cards today. Perhaps we'll never know the true identity and story behind the man named Saint Valentine, but this much is for sure...February has been the month to celebrate love for a long time, dating clear back to the Middle Ages. In fact, Valentines ranks second only to Christmas in number of greeting cards sent. Another valentine gentleman you may be wondering about is Cupid (Latin cupido, "desire"). In Roman mythology Cupid is the son of Venus, goddess of love. His counterpart in Greek mythology is Eros, god of love. Cupid is often said to be a mischievous boy who goes around wounding both gods and humans with his arrows, causing them to fall in love.
So based on the above text, we as Muslims, must not celebrate Valentine's Day, as imitating the Kuffar is strictly prohibited. From the above article, we know that Valentine’s Day has its roots in the Christian religion. It was established to mourn the death of a Roman priest, Saint Valentine of the third Century AD. Since Valentine’s Day was initially associated with Christianity, the expression of love in the form of exchanging Valentine’s gifts and its related activities on that day will not be permissible.
Rasulullah SAW said:
"Whosoever imitates a nation, is amongst them." (Riwayat Abu Dawud)
And for those who are involved in the of purchase or selling of gifts specifically prepared for Valentines, let it be known that this too is also Haraam.