I don't think I'd give him the letter. Right now, surprise is on your side, and I'm guessing your H doesn't have a clean pair of underwear for all the freaking out he's doing. It's better for you legally to have the surprise factor, keeps him off balance.
Plus...why? What does it get you? It feels designed to get a response rather than inform, and I say cross the information bridge when you need to.
You sound amazing, by the way. Getting clear and letting go of others' crazy is empowering! Keep it up~you're a rock star!
SD
Me: 40 H: 43 H had EA from 2/06-9/06 Bomb 5/06 Piecing since 9/2006 3/2008: Boundary setting 7/2009: Boundary crossing~dropped my own bomb. 8/2010: Marriage finally on track!