Hm..interesting question :) Not really sure about the comparison between partners, at least I didn´t see any of studies like that. I bet there it would be a difference between man and women :)
I know for the Richard Schwartz and Jacqueline Olds study where they analyze evolution and collapse of the love. Also, Helen Fischer study love after decades of marriage and clamed that " the excitement of romance can remain while the apprehension is lost". :)