He doesn't have a backbone now. Maybe he'll grow one when Marge dies and ditches Mary for Katja. That maybe wishful thinking
TBH that would not be the solution. It is not only Mares that is wrong (for him). He can't fit the shoes ... And like her or not but Daisy is doing a great job as a royal. Even now after losing the love of her life she is able to interact with people, show her face, function. May he fashion choices be sometimes extraordinary, she is regal to the ground. Plus she is pushing the 80s as well but she is there, present, functioning and working ... all things Frodo does not do.
If it is was just the unhappy marriage he could be actively working along his mom, supporting her, be a great and loving dad (even the dad he never had) to his four children ... but they had to install Jokke and Marie because he is not working ... at all most of the time.
Fred needs to grow up, find some direction and take responsibility for his life. For too many years, he has lived his life as a 20 something frat boy who has years to to get his life in order.
He seems to have failed to realize that the years continued to pass and he is no longer that 20 something prince.
With Henrik's passing, maybe Fred will have an epiphany of sorts, gets some professional help and finally get his life together. If not for himself then for the sake of his children.