Jacopo da Ponte - St. Valentine Baptizing St. Lucilla (Wikipedia)
"Grant, we beseech Thee, O almighty God, that we, who celebrate the heavenly birthday of blessed Valentine, Thy Martyr, may by his intercession be delivered from all the evils that threaten us. Through our Lord." - Roman Catholic Daily Missal, 1962
St.Valentine (Valentino) was a Roman priest who performed marriages in spite of Claudius II's law against such (Claudius believed that marriage was distracting to his soldiers, so outlawed it to them for a time). Fr. Valentine was martyred in A.D. 270 on the Flammian way, and at the site of his martyrdom, Julius I built a popular basilica.
Other than this, little is known. Because two other St. Valentines share this Feast day ("Valentine" was an extremely common name for Christians as it has the same root as the word "valor"), often their stories are confused, but it is the Roman priest-martyr whom we honor during the liturgy.
St. Valentine's skull is in Rome, but other of his relics -- at least a great majority of them -- are, interestingly enough, in the Whitefriar Church associated with the Calced Carmelites in Dublin, Ireland. They were excavated from the Cemetery of St. Hippolytus, on the Triburtine Way in Rome in 1835 and were then given to Fr. Spratt, an Irish Carmelite, by Pope Gregory XVI in 1836. The relics, "together with a small vessel tinged with his blood," were deposited "in a wooden case covered with painted paper, well closed, tied with a red silk ribbon and sealed with our seals and we have so delivered and consigned to him, and we have granted unto him power in the Lord, to the end that he may retain to himself, give to others, transmit beyond the city (Rome) and in any church, oratory or chapel, to expose and place the said blessed holy body for the public veneration of the faithful without, however, an Office and Mass, conformably to the decree of the Sacred Congregation of Rites, promulgated on the 11th day of August 1691," as the letter accompanying the relics reads. On this Feast Day, his relics are carried in procession, and a special Mass is offered for young people and lovers.
The Novena to St. Valentine can be prayed always, but is especially prayed starting on February 5 and ending on the eve of his feast today.
Because of his Nuptial Masses, he became the patron of lovers, the affianced, and married couples, and fortuitous to the priest's association with romance is the belief that halfway through the month of February, birds choose their mates, hence St. Valentine's association with birds, especially lovebirds and doves. Chaucer mentions this belief in his "Parliament of Foules":
For this was sent on Seynt Valentyne's day
Whan every foul cometh ther to choose his mate.
Also fortuitous is the fact that red is both the color of Martrys and the color associated with love. Red roses are also a symbol of both martyrom and love, and had also always been associated with the Roman godess of love, Venus.
Venus' son, Cupid ("Eros" in Greek), god of love, was originally depicted as a very handsome young man, but now as a winged putto bearing a bow and arrow with which to smite hearts with love. His image, along with the image of hearts he has pierced with his arrows, are ubiquitous symbols of romantic love on this day.
St. Valentine's Day cards are a very ancient custom; one of the oldest extant "valentines," as such St. Valentine's Day greetings -- and the persons to whom they're sent -- came to be known, was sent in 1477 by Margery Brews to her fiancé, John Paston, and can be seen now in the British Museum. It reads:
Unto my right well-beloved Valentine John Paston, squire, be this bill delivered.
Right reverent and worshipful and my right well-beloved valentine, I recommend me unto you full heartedly, desiring to hear of your welfare, which I beseech Almighty God long for to preserve unto his pleasure and your hearts desire.
And if it pleases you to hear of my welfare, I am not in good health of body nor of heart, nor shall I be till I hear from you.
For there knows no creature what pain that I endure, And even on the pain of death I would reveal no more.
And my lady my mother hath laboured the matter to my father full diligently, but she can no more get than you already know of, for which God knoweth I am full sorry.
But if you love me, as I trust verily that you do, you will not leave me therefore. For even if you had not half the livelihood that you have, for to do the greatest labour that any woman alive might, I would not forsake you.
And if you command me to keep me true wherever I go, indeed I will do all my might you to love and never anyone else.
And if my friends say that I do amiss, they shall not stop me from doing so.
My heart me bids evermore to love you truly over all earthly things.
And if they be never so angry, I trust it shall be better in time coming.
No more to you at this time, but the Holy Trinity have you in keeping.
And I beseech you that this bill be not seen by any non earthly creature save only yourself.
And this letter was written at Topcroft with full heavy heart.
By your own Margery Brews
To send a very Catholic valentine to someone you love, how about using a paraphrase of today's Collect as the basis for the text?
Grant, I beseech Thee, O almighty God, that (Name of loved one), who celebrates the heavenly birthday of blessed Valentine, Thy Martyr, may by his intercession be delivered from all the evils that threaten (him/her). Through our Lord Jesus Christ, Thy Son, Who liveth and reigneth with Thee in the unity of the Holy Ghost, one God, world without end.
...with all the personal, mushy stuff at the bottom! For a romantic card for a spouse, some of the poetry found in Solomon's Canticle of Canticles -- a Book which uses marital love as a metaphor for God's love for His Church -- cannot be surpassed for inspiration.
On this day, the giving of roses is standard (consider offering Spiritual Bouquets, too), and as to foods, oysters, chocolates, champagne, and heart-shaped foods are all considered to be romantic.
And a note to all: be sure to wish people "Happy Saint Valentine's Day" rather than just "Happy Valentine's Day." This will help bring the deeper meaning of the day into focus!
Commentary by Fish Eaters, here.
In Christ Crucified and the Most Victorious Heart of Jesus.