What could be worse?

I had a good day yesterday when I completed and submitted the tax return. I live overseas but still pay US federal income taxes. Every year the tax laws change some. But this year the change is on my side---the time I typed in my wife's name and SSN, I cried and stopped. But finally I was able to assemble enough willpower to complete it. Today is not that good. Going out for lunch with couples with whom my wife and I used to dine was tough. These people are very nice. But the problem, I guess, is me.
I have two dominant emotions recently. Sadness has been a common occurrence. It often starts in the early morning and I often carry it the whole day. Sadness is not pain, at least not deep pain. Sadness is like a grey cloud but pain is a darker wave. Sadness hangs over your head and pain penetrates your heart. Sadness, accumulated,  does lead to pain. 
The second emotion is uncertainty about the future. I know I shouldn't be worried about things 2-3 years down the road, but my problem seems to be more acute because I live in HK--a forever transient city. The thought of uncertainty always came out when I heard colleagues talking about going back to the US or UK...Where am I going to be 2-3 years from now? What am I going to do in my future? A psychiatrist told me that uncertainty is cause of anxiety which can lead to fear--fear for the future. Oftentimes when this happened, I said to myself. My wife has just gone. The worst has happened. What have I to fear that can compare with what I have already lost?