A relationship between two people is a dynamic process. A lot can change over time. The intensity of physical desire may wax and wane through to years, only to wax again when you least expect it. At times, the most predominant feelings experienced by individuals in the relationship may be frustration or boredom. At other times, excitement and gratitude. Later, feelings could be become conflicted, complex. Boredom and gratitude, perhaps?
A relationship may seem to coast on past energies for a period of time. People change, priorities change, responsibilities change. Relationships move in cycles. For long-term relationships, renewal is perhaps the most important of these phases.
Through it all, a relationship can tolerate the expression of a lot of different feelings: joy, anger, confusion, contentment, boredom, desire, disappointment, respect, disrespect, patience, impatience, distraction, embarrassment, envy, acceptance, trust, distrust, wonder, defiance, satisfaction. Just to name a few. All of these feelings will be experienced at one time or another by individuals participating in a long-term relationship. Some of them are certainly more pleasant than others. There is a place for each in a loving relationship. Some are necessary and sometimes painful signposts on the way to a deeper level of understanding and love.
But there is no place in a loving relationship for scorn. Scorn is a relationship killer.