It simply means: sucks to miss you, still.
Describes a feeling of loss that you can't control and can't explain. It can happen at any moment
without warning. When
enough time has passed and you should be "healed" and moved on...but you have these moments of "what if" and "if only". It also describes the regret felt when you aren't right for that person and vise-versa however, you still miss them
in your life.