Patricia,
Great to see you working so much. There are several things that can be done to improve on this. Some of my points might have been addressed as you went on, so feel free to disregard some of them.
Immediately, the jaw line on his left looks off, which makes the right side of his face dip. The shape of his ear is also a bit off, there should be more lobe. Double check the way his nostrils line up. The forehead may also be too big. What I just wrote may also be attributed to the angle the picture was taken, so what may seem off, may be just fine.
If you have a problem going darker, you should start with a value sketch on cheap paper. This is a great ref pic for that type of excercise. Once you break down the drawing to simpler values, it's easier to determine when you have to go dark.
I'm sorry to be nit-picking, but the double shirt line does not have the same flow as the rest of the picture and is distracting. Lightening them would help, or going darker first on the face may make them not as noticeable.
Please post an update if you decide to take this further.
Jimmie