The notion that "guessing" and "misunderstandings" are wrong when it comes to a romantic relationship is a flawed perspective. There will always be moments where both partners are unsure of what their partner means or are unsure of how to navigate a situation. This is simply part of being in any relationship. Even if both parties are always there for one another, they will still be uncertain and make mistakes at times.
Though it's true that a romantic relationship will not have an ending like an improv performance, it certainly can have moments where one partner takes the other's place during a certain scene. For example, while one partner might be having a tough time, the other can step in to take their place and weather the storm on their behalf. This act of selflessness and support is what makes relationships so special, but it does not make them any less similar to improv performances.
It's true that romantic relationships involve deep connections between two people, but this does not mean that they are completely different from improv performances. Both involve guesswork, misunderstandings, and someone else taking your place occasionally - this is what makes them so exciting! To suggest that these elements do not exist in relationships is wrong - maybe not all relationships will have these elements but they're definitely an important part of any kind of partnership. So while it's nice to think of relationships as beautiful and eternal, it's important to remember that they have their similarities to improv performances too!