I think my husband should keep his mouth shut?

If you feel she's your aunt, and that's the relationship you have with her, then she's your aunt. I think the point your husband was trying to make was that from a "technical" by-the-book standpoint, she's not "really" your aunt. Your parents siblings are your aunts and uncles, and their spouses become aunts and uncles by courtesy. When the marriage ends for whatever reason, some drop the title. Others don't, and it's a matter of personal choice for those involved.