Chris,
Let me answer your questions for you.
He walked out on you the way he did because he did not want to face you and have to explain himself. He did not want to see you cry and try to hold him back. He did not want to admit that he is no longer in love with you to you. He didn't want to deal with you and your “issues.” That is why he left the way he did.
Now, he's ignoring your calls because he owes you nothing—no explanation, no talk, no apology—NOTHING. You and he both did not sign a contract about needing to have a “last talk” before you two part ways. Yes, you two agreed to one last talk but it is a free country and he is a grown man with the ability to change his mind as he pleases. HE CHANGED HIS MIND. What can you do about it? You can do NOTHING to change his mind about having a last talk.
HOWEVER, what you can do and probably refuse to do these days because you're so caught up in the emotions is MOVE ON. You have the freedom to move on but you have to find your want and your strength to actually move on. You are in the mourning stage right now so take the time to mourn and cry all you have to but make sure that once all tears have been cried and wiped away, you pull yourself together and keep on treading along in life. No one said it will be an easy process but I can guarantee you that we will all tell you that you WILL and CAN get through it.
Also, please try your best to not ask yourself all these questions that will do unanswered. You are only hurting YOU, not us and especially not him. By you wondering and pondering about all of these questions is driving you mentally insane and emotionally destroyed. So what if he ignores your calls, it's his loss. So what if he didn't give you an explanation—that says something about his character, not yours. So what if he is no longer in your life—be happy that you and he at least had time together.
Now answer my questions.
What was the best thing he ever done for you?
What was the worst thing he ever did to you?
Where do you see yourself 5 years from now?
Do you really want to be with someone that left you behind without bothering to turn back around to make sure that you're okay?
Do you really want to be with a guy who walked out on you without an explanation?
Do you really want to be with a guy who couldn't give you the truth regarding whatever issues you two had?
Now, what if you spent all of your time crying over him and for him and wishing, wanting and thinking you need him that you let a guy who is as amazing as your ex if not better walk past you?
Think about it, some women go fishing for fishes in the sea while others go fishing for a merman. Which one to do YOU want? A fish that can swim away as quickly as you caught it or a merman that will stay for long as it took you to find it?
Again, best of luck to you--keep your head up. There is always a rainbow after the rain.