I personally think some sentiments should always be present unless the relationship has reached a very bad state to make them go away. The adoring sentiment is that one that I hold the biggest issue with...
A parent should never loose the adoring sentiment for their child unless the relationship between parent and child has reached a very bad state, same with siblings or pretty much anybody that gets this sentiment for another sim and the relationship is being maintained in a good state. I don't believe this sentiment should just fade away while the relationship is still good, it makes no sense for it to fade away with time.