Because sweetheart, hes cunt, a selfish, stupid, bullying, manipulative cunt.
Dont let him drag you down to his shitty levels, your so much better than that piece of shit, you should feel proud of yourself, being a single mum, doing a great job, got into college, your life is starting to right itself.
Wipe your hands of this man, if wants to see DD, then hes gotta learn to ask nicely and if he doesnt then he dont see her, and if he keeps on with this shitty behaviour then call the police and show him the evidence.
He wants to control you, because he knows your life is changing, your changing, he could manipulate the old you, this new stronger you, he cant get too.
So look at the message now, and say loudly to youself, "Oh just fuck off you cunt" and shut it down.
You are better than this man, remember that.