When a relationship dies, a part of you dies with it too. You wake up one day and realize you can no longer call this person and hang out like you used to, and that hurts to the core.
In that phase where you start to accept that you actually broke up, you will miss them greatly. You might go through some old photos you took together before you delete them, wear their jumper one more time, and before you know it, you've been stalking them on Instagram for the past three hours.