Well, this isn't exactly one of those situations. As I understand it, (1) there was no "family" for Noel Miller to abandon (she and Andy Christie, the bio father, split before their baby was born), and (2) Casey Frederiksen is/was a very close friend of Christie's and I gather he has pretty much been by Miller's side since Evelyn's birth.
I suspect the use of the term "fiance" to describe Frederiksen is contributing to the readers' misunderstanding of these facts. He's been around long enough to father two children by her; has anyone seen mention of a set wedding date?
She has been wearing an engagement ring for a number of years, since before Gabriel (age 2) was born. Noel once said she wanted to wait to get married to save up the money to have a big wedding. Some speculate Noel would never marry anyone since that would mean the end to some of the public assistance she was receiving.