Yes, St. Valentine was real!!
He was an early Christian martyr in the 3rd century. He was of the category of saints called "Holy Unmercenaries". Basically this means a physician saint who took no payment for services. He became friends with a Roman jailer and his blind daughter. He prayed for the daughter and tried healing her with various ointments, but to no avail. They picked flowers together and became fast friends. During one of the persecutions, Valentine was arrested. While in jail, the jailer heard of his imprisionment, and came to him. Valentine wrote a short letter to the jailer's daughter and the jailer promised to deliver it. The daughter opened the letter and one of the flowers they had picked fell out. The father read her the letter and all it said was "From your Valentine". The girl then miraculously regained her sight.
In the Orthodox church we celebrate St. Valentine's memory on July 6.
Here is a link to a wonderful icon of the saint: St. Valentine from Come & See Icons
Also, here is a children's book I picked up at a local bookstore that tells the story using mosaic art to illustrate: St. Valentine