@strictlyanonymous728,
Really hard to know. "Early last summer" sounds like it was around this time of year... while I haven't experienced this myself, I know that the first anniversary is a particularly hard time.
But this could be happening for any number of reasons unrelated to the fact that he's a widower, too. I think he's the only one who can tell you what you want to know. Why not just ask him, for example, "Does your message mean that you have decided you're not ready for a new relationship?"
Are you comfortable with keeping something casual for a while until he knows one way or another, if he doesn't know yet?