Erasing all the memories of you ex partner is one of the difficult challenges people face while going through a break up.
The pictures the videos all represent good memories you shared together with that person, but you are trying to move on and get over that person, keeping those memories will not only weigh you down but it will stare up pain again inside you, that is why no matter how difficult it might seem at the moment you have to try by erasing all of it.
So you can be able to move on, keeping those memories means you are still clinging to the past and you don't want to find a better chance at love.
When you are certain you have cleared and erased all the memories you can move to the next step.