Have you asked him to sit down and talk to you about what was missing for him where he decided to move out?

Moving out doesn't always mean "end", it can be more of a way to say "you don't seem to feel I am important and I feel lonely in our relationship". Usually in a healthy relationship each person has things they do separately but they connect by having certain things they do together and enjoy doing together that creates a very important sense of "companionship". They stay together because of the companionship they experience, without that a person begins to look elsewhere.