Having a light contact every now and then like, a short email or phone call once a week is very different than spending a whole evening together holding hands and feeling miserable about what you two think you lost.
There is an exact measure you have to discover.
If in doubt, focus on other social connections rather than your ex.
Remember that he is part of your past, not your future.
Rebuilding something on the ashes of a broken relationship is very challenging.
Most of the times, it is simply easier to move on and find a 100% new and fresh ground.
That's certainly what I would encourage you to do.
To your power!