A fundamental difference between love and lust is the level of sharing.
When you are in lust you will only share things down to a certain level but for the most part you will not share things that are part of your core.
When you are in love you will share all the way down to your core.
Have you been married for years but have some secret down in your core that you have been holding on to that you have not shared?
It may be forming a wall that you are not aware of in your relationship.