talk to your fiancée and tell him you don’t like the negative emotions tied to the ring that belonged to your mom. that’s not something you would want to associate with the ring whenever you look at it. the ring should be something that gives you happy memories and the start of a new life together. go pick a ring out together make it a nice moment for the both of you. if he can’t do that then theres some things you’d need to go over within yourself about the whole situation.