Some things turn out to be harder than you expect

I just wrote a letter to my last client telling them that I have shut down my consulting services and they should look elsewhere for administration and support for their servers. It was harder to do than I was expecting. These guys were my cornerstone client for years, but I don't do the work they need anymore. Despite being aware that it's misplaced sentimentality, it still feels deeply weird to tell them I'm out of business.