People say things when they are angry that they wouldn't normally say and forgiveness in some is very hard. What you need to do is no contacting him for at least a week because the wound is still fresh and when you text and try to contact him it just adds salt to that wound and makes him think about everything you said all over again. He needs time to get over the anger, So what I would do is tell him again that you apologize and list everything that you said or did that you are sorry for this way he knows that you acknowledge everything that you did wrong and will be more apt to forgive if he thinks it's sincere right now he thinks you are only saying this because you know you are losing him and he doesn't believe that you are sorry. He was blunt with you because he is still angry at the things you said to him and wanted you to hurt like he hurt, sometimes words can hurt more than physical actions because they hurt to the core of the person's being.
First thing to do is write him a long email or letter stating why you are sorry and the things you are sorry for, then give him time at least a week, this will allow him to think about things more clearly, also when you start working with him on Monday don't try to talk to him about the relationship but keep the lines of communication open by at least speaking to him when you see him don't totally ignore him, if you ignore him it will only make him more angry but don't try to carry on a conversation unless he starts the conversation first only say things like "Hello" and "Bye" or "Bye have a nice evening" this will show him that you are at least making an effort to be nice and cordial while at work. Last and MOST important let him see the person he fell in love with in the first place go back to the things you did that made you special to him, he didn't like the person you were when you were being mean so lose that person even if it means going to counseling to find out why you turned on him. Be patient it's going to take some time to get him to even consider forgiving you so don't do anything (like dating someone else) that will jeopardize getting him back.