In other cultures, nursing is the norm. Although three years is not a common age for children in the United States to nurse, it has been the norm for you and your daughter, as it has been for us. This is a challenging stage of life for children. Their verbal skills are developing, but a child this age still cannot fully express his or her needs or feelings. With nursing, no words are necessary.
Nursing allows both the child and mother to take some time-out to regroup and reconnect.
I have found nursing to be an invaluable parenting tool, especially on those trying days when my patience is thin. Also, tell him that no child nurses forever and that soon your child will move away from nursing more and more. I can attest to that. If so, you may want to consider sharing this information only with those who understand and are supportive. I know it can be a challenge to nurse for an extended period of time, and I admire you for your efforts.