Clothes make the woman
Not knowing your husband, it’s difficult to say, but I’ll throw out a few ideas. Could he be insecure or intimidated by your professional image? Could he be jealous on some level? In what kind of environment was he raised? Was his mother’s “uniform” a housedress?
If you are earning good money and your family is being provided for, then you are certainly entitled to spend some of it on yourself. And you shouldn’t have to apologize for it.
It’s YOUR name. So do what you are most comfortable doing, because it’s the name you will have to carry until the day you die (or divorce).
Being “in love” shouldn’t cause stress; it should relieve it. You know what you are doing is wrong, and YOU must be the adult and end this relationship. If you don’t, it will bring heartache and turmoil to you and the rest of the family. By having an adulterous and incestuous affair with you — her nephew and a minor — your aunt is behaving like a sexual predator.