Gosh, this really got to me too. This definitely is a bittersweet moment, and I'm sorry that you and David are likely to not stay in touch, so I know you will miss these 3 darlings.
I'm glad that you're confident in the fact that David will take good care of them though, so they should be in good hands. You're doing what's right for everyone involved: you, David and the kitties and that's what matters most.

Lots of love and **hugs**
Karen