[jklein11]

Call me a millennial but this is an extremely odd view of the world to me.

Everyone is unique. Everyone has had a different set of experiences that brought them to where they are today.

Relationships are also unique in this way. They are a shared set of experiences you have had with another. Each set of shared experiences is unqiue.

In the case of the OP, only he and his current SO will have lived through making this decision with each other. The strength of their relationship going forward will be in part because of this shared experience.

Are you arguing that it is possible that the SO would be happier if they were making this decision with the other person? I'm sure that this could be theoretically true, but it seems somewhat irrelevant.