Or, re-kindling the fire. Blowing on the ember refers to the following analogy. "One time, there were a group of campers, who were friends. One of them decided to light a fire, so he did and everyone was happy for him. Then, it was time to put out the fire, so he did. During the night, the camper felt lonely, so he saw an ember still in the fire, and blew on it to ignite a spark and start the fire back up. The campers didn't like that, so they beat up the other camper and kicked out the fire.
It refers to when a person is trying to re-ignite a relationship that others feel should not be re-ignited.
Alex man, you gotta stop blowing the ember. Shes a bitch and you know it.