Why do you think you need to see the world from someone else's eyes to like them, and convey the emotions one feel toward them adequately?

Knowing people to the core is a continuous and a long process, and probably cannot be achieved as everyone has their unknown dark secrets, thoughts, and experiences. Only the days and circumstances will reveal a person gradually to a certain extent.

But I believe people's basic traits that dominate their personality can be known with proper probing.

You don't have to be alone because of a life's fact that every one is a unique person.

Was what you knew about your partner the reason you ended the relationship with them?