The one main thought that comes to mind is he is indeed depressed, and it's his depression talking to you, not the real person inside. His depression is clouding ALL of his emotions, even his feelings for you. It is very hurtful to hear the words, "I never felt anything for you, and I don't even now", but you know that given his behavior all this time, that this is not true. So please believe and know that it's his depression coloring his perception and even his words and feelings.

At this time, there's nothing you can really do. You cannot force the relationship, and it's best to not hold onto a sliver of hope. The fact that things turned around a complete 180 degrees is not a good sign for a hopeful future with this person. I would not bank on marrying him or being with him long-term, even if he does come around. Sorry if that sounds harsh, I am just saying it like I see it. IF someone can turn on you like that and dump you in this kind of manner, they are not a good future investment, you see my point? There's no stability in that kind of a relationship. He is not emotionally well. But do take solace in knowing that his words are not true. Based on what you've written, he definitely cares for you and I am guessing loves you, he just cannot be in a relationship.