You could pose with something Valentines themed to cover you if you want it to be sexy and valentine's themed. This would be implied, so I don't know where you stand.
http://i.istockimg.com/file_thumbview_a … -shape.jpg
You could do a shoot of all the things you love about him, like a story line, if you want to be cute.
Something he loves like a sports team or a hobby? Do a sexy version of that.
Guys aren't particularly picky about these things. He'll love it just cause its you.