The guy broke up with you because you wouldn't abort your baby. I wouldn't even think about giving the baby his last name. I wouldn't even want him around the child for a while. If he did decided to see it my first comment would probably be "oh, but I thought you wanted me to kill our kid before". Don't even think about giving the baby his last name. Think about it.
He broke up with you for not killing the child you want to have! It should be an instinct to protect it. That means keeping it away from people that want it murdered!