I think your question is a good one and it's a shame no-one has replied yet.
My husband and I have had our low periods - nothing too serious, but we have had our times of disappointment and disillusionment. I firmly believe you can get through those even when any romantic feelings are missing and you are feeling hurt.
I think you are right that it takes two, but one can start. one of a couple taking the trouble to do loving things and speaking positively and refusing to take offence can begin to turn the tide. It can be hard work sometimes.
When my husband was made redundant he did some of the most bizarre things and I was feeling very frightened and insecure, but I managed to stay strong for him and give him space to work through his pain over it. It was a tough time but we came out stronger.
I have also come across people who have been badly hurt and yet have rediscovered the feelings for their loved one by choosing to stick by them and look for the good in them. I think some of it is to do with being at peace with yourself and not looking to the other to fulfill your needs all the time. For me that comes from my faith in Jesus - I always have him to turn too when others let me down.
I wonder what others think.