Liz, When you lay out the evidence there is a perfect reason for his behavior.
1.In a lot of pain
2.Trying to quit an extremely addictive habit(Smoking)
3.Dealing with a life threateninmg disease (cancer)
4.The biggest reason of all- He's a MAN.
1+2+3+4= Major league A##HOLE.
The above formula leads us to #5-- Somehow we find a way to get thru this craziness, you have a lot of help here. Expressing your feelings is a good way for you to feel better, Keep up the good work.
Always,
Mark.