Yeah, I got a letter just like that from my soon-to-be-ex. Often it is a projection of what they themselves are thinking or doing (try switching all the "you"s to "I"s in his communications, sometimes it really gives you a window into their minds).
You handled it beautifully. Reassure him that you want to be reasonable, point out that this is just what the law allows. The law is there for a reason.
And be sure to speak with your attorney, make sure what you're asking for is reasonable and fair. If it is, his attorney should tell him so.
