It can be so confusing when someone, we are in relationship with decides that they need to separate simply because, they are not ready to deal with another person’s issues, or their own issues.
Those who do not want to deal with their issues have a tendency to pass them onto someone else, then they can pretend, they do not have them anymore.
They expect their relationship to be perfect without its down. Some can clarify, who they are while in a relationship, but not everyone can.
In some cases, some really do need to separate in order to find their individual identity. Especially, if they are not at peace with their individual path, they will not be healthy attuned nor reliable partners.
If there's a possibility that they may return, you have no way of knowing, who they will be then.