Understanding nonverbal communication in romantic relationships can be one of the most important factors in whether it succeeds or fails. Understanding what you partner likes and doesn't like makes all the difference in the world, and if you can read the cues they give you, you will know immediately
if this is something you need to continue or cease doing. Everyone wants to be with a partner who cares about their feelings and understanding nonverbal cues is incredibly helpful in understanding your mate.
As couples spend more time together, they talk less, and rely more on non-verbal communication. For it to work, both parties must grasp what the other one is "saying." Non-verbal communication is also based on routine, which leads to stability for many people. If words always accompany an act, then the act is done one day without the words, the receiver knows the message.
Yes, I do believe that understanding nonverbal communication is one of the most important factors in maintaining a successful relationship. A bigger portion or our communication is non verbal than most people think. I think that people who are closed off to understanding each other verbally and non verbally are probably more destined for divorce.
A successful romantic relationship can exist irregardless of whatever state of nonverbal communication exists. The question is too general. Each couple would have to be studied to determine whether nonverbal cues exist. A certain couple,placed in a romance inducing situation, might display no detectable nonverbal cues yet experience true love and affection.