My husband has had diarrhea for 3 months. he waited too long to see a doctor could this be fatal? he is now anemic.

Get worked up: Your husband might have a chronic bacterial infection, amebiasis, Crohn's, Whipple's, tropical or non-tropical sprue, a villous adenoma of the colon, a VIPoma / gastrioma or a few dozen other fairly common entities. He needs to be under the care of a competent gastroenterologist; his primary care physician can figure why he's anemic for now. Ignore this & he can indeed perish.