Op, so he's openly texting in front of you with this woman.
Very disrespectful, even if it's to tell her it's ending, maybe he is implimenting damage limitation so she doesn't pop round, but i'm not so sure, he sounds a pretty cocky character.
Nobody can tell you whether he will stay, i personally think he will but he's a twat of a cake eater and he's presently seeing how much you will take, and at the moment you are broken, destroyed by his inhumane treatment of you.
My advice would be to build yourself up, stabalise and gain strength whilst he plays his merry dance of finding himself irresistable, you don't have to make a decision at the moment, wait till you have picked yourself up off the floor.
These things take time, you don't have to sort everthing out and decide, do it when you are ready.
I hope you have support, confide in someone.