o.k. I am also not sure who the step parent in this situation is either... but I will say this, I think there must be a special place in heaven for step-parents (the good ones anyway). my step-dad is the greatest... and while i still love and speak to my father, my step-dad... well, he's "my dad" if you know what I mean. much more involved in my life than my dad ever was.
anyway... growing up I gave both my dad and step-dad cards that said "happy father's day" or "happy valentine's day dad" my whole life... both of them gave me away at my wedding (though it did look a little strange). anyway, I'm just saying... this guy, is being his "dad" so why not honor him that way.
and specificaly speaking on valentine's gifts.. last year my daughter gave her dad two books:
"daddy kisses" and "I love my daddy because..."... both are animal books, she loves them.. and they love to read them together. (they have mommy versions too). anyway, my husband really was touched by receiving them. plus they weren't very expensive.. and better than having a bunch of chocolate laying around the house that I'd just end up eating.