This is an intriguing question, which is why I chose to respond. It's really a personal decision between you and your husband, but presumably you know that.

Presumably, you are also already producing breast milk. If you aren't, I doubt you could breast feed anyone without the stimulation (perhaps medicinally) of certain hormones.

If you are producing breast milk, then increasing the number of people you give it to should only stimulate the output, not decrease it.

Breast milk is specially formulated by the mother's body to match the needs of the infant the mother gestated. Therefore, it is the ideal nourishment for your baby particularly, but a great form of nourishment for any infant if you should choose to become a wet nurse for the infant of a friend or family member. Unless your husband has some sort of unknown allergy, it should not cause him problems, either.

The only real obstacle to you breast feeding your husband is your personal ick factor. If you and your spouse find it arousing and an action that brings you closer together, than do what you like. If either your or your spouse are discomfited by it, than don't do it, and don't allow yourself to be pressured into it.

Edited to add:  A word on some of the comments.  I have had to delete some comments, although it goes against what I strongly believe in for free speech and journalism, because they had no editorial relevance to the article itself.  Please do not post comments that share intimate details of your sex life with your S.O., including the length of time s/he may like to suckle, what marks their enthusiasm may leave behind, or what positions they may like to do it in.  While hubs readers and I both appreciate the knowledge that this is a normal and regularly practiced activity, one of the beautiful things about an intimate and private sex life is that it is intimate and private.