What does it mean when you think about an ex pretty much daily?

Means nothing.
Just your head trying to fool you into thinking how wonderful life was back then.
Which of course it wasn't or you'd still be together.

For me, never go back... You may still have feelings, but there's a reason he's an ex

There's obviously -some- element in his persona or behaviour that you are craving, feeling the lack of in your own life. Maybe find someone who can supply that, without your ex's obvious drawbacks?

You're not over him.
OR most likely, you miss the times you used to have with him.

Maybe you need someone else who is important to you in your life.

Fond memory ☺

That you are still in love with him.

You need to go play the field and give into lust a little bit.