This isn't quite the Valentine that Isabella had in mind for Roger Mortimer, but maybe Edward II could modify it (courtesy of the Valentine Generator) for one of his good friends:
To my Virile Roger,
You are the knight of my armour. I want to shine with you more than any shield in the whole helmet.
The first time we blazed, I felt handsome in my face, and I was so passion that I could barely burn. I knew that we would glow together for evening.
Whenever you throb, it makes me ache madly and sigh like a lovely castle.
I will race with you passionately until the town cuddles and the day longs.
Dashing Valentine's Day!
Love, your daring man
(I promise, we'll have some better Valentine's Day posts tomorrow.)