Chewing will irritate the esophegus, thereby causing you to cough. It simply attacks different parts of the body is all. Tobacco is bad, period. Call your doctor about the cough. 8 years! Wow! I bet you are kicking yourself. I understand how hard it can be to be around smokers in times of stress. My heart goes out to you!
First off call your doctor. Chewing tobacco is just as bad as smoking, if not worse. It could be your lungs clearing out, but it could be the juice from the chew getting into your lungs. So call your doctor just to be safe.