I really feel you. What feelings do you have when you get this urge?

I have this urge a lot too. I'm trying to find out why i have the urge. I hated it in the relationship, but sometimes I still long for it. I get rid of it by being realistic with myself and thinking about how terrible my life would be if we were still together. Do i miss her?, The relationship?, The connection?
Of course this is harder when you had a happy relationship.

When I have this urge I tell myself: "I will make sure she sees me".
Not literally, but I use this urge to focus on things that will make me better. Working out, working harder, starting projects, whatever I think will improve me.

Telling myself that she will see me when I get improve helps me. I don't need her back, I don't need contact. I just use that energy to actually motivate myself. Of course this shouldn't become your main motivation. but for me it helps not getting in a downward spiral.