Honestly? Are you proposing seriously to discuss when a widow or widower is allowed to be happy again?
Let me be clear: I have no intention of looking for another husband. I love the one I had for too short a time, and at 73, I don't feel the need for a new man in my life. My husband told me when he knew he was dying to promise him I would enjoy the rest of my life and do whatever I wished, and that included a lover or new husband. I would have said the same to him, if I had been the one to go first,
But that's just me.
It is the business of the bereaved person and the person who comes into their life, or assumes a new importance if already known, if they want to live together, marry or just be good friends.
It does not, and cannot, concern anyone else.
Do you go telling those poor souls who have lost a baby, or an older child, when it would be "decent" to try and have another child?
If not, why are you bothering about what widows and widowers choose to do and when they choose to do it.
Be glad that the bereaved are still able to enjoy their lives!