Ex left, told son unsure when he would see him again. Advice?

[wonderstuff99]

Basically my prick of an ex left on Saturday after an incident which involved him nearly punching me and preventing me from leaving the house. We were separated anyway and my son knew he was going to be moving out soon. But on Saturday, he told my son he was leaving on Sunday and wasn't sure when he would see him again, as in, I'm disappearing from your life. Our 4 year old then preceded to tell for the past few days, me he feels he doesn't have a daddy anymore (heartbreaking) and I actually don't know what to tell him.

At the moment I'm going down the route of, you will always have a daddy, it's just that daddy has gone away to learn how to be a good daddy. But I don't think this is going to cut it. It's his birthday next week and he was saying, oh, maybe Daddy won't be at my birthday party either.

My ex isn't the kind of person who apologises when they are in the wrong and does what is best for their son. He's the kind of person who says things to him to hurt me (a fuckhead basically) so it's not as if he is going to be willing to sit down and have a discussion with me about this. He's at his sisters at the moments 100 miles away from us and I know if I ask him his plans and what I should tell Isaac, he'll just say he doesn't know.

I know I can't give my son any definite answers, but it feels awful to just keep him hanging. Yes you have a daddy and he loves you but...we just don't know if you'll ever see him again?!!

Any advice on how to make this easier for him?