Damn 19 and you got a wife and a mistress?
Say you love her so much that you want to be with her for eternity, then pull out a knife and chase her screaming that you should die together and to come back.Works like a charm.
A poem in the card written by yourself + heart shaped chocolates/flowers should do.
Don't fall for the whole valentines day crap. Its none only than a holiday for hallmark to make money. Sit at home with the lady watch a movie and eat some popcorn.