I miss him and it hurts

I am struggling to emit the noise of my head and the thoughts that are consuming which all revolve around him and the what ifs and the fantasy I'm in love with.. It's only been 3 weeks since I've been discarded unexpectedly and replaced with him moving someone else in two days later and me seeing them holding hands all happy two days after that!
All the good stuff floats to the top and I can't let it go ( even though the bad out weights the good!) he (and her)constantly are in my mind and the fact that I don't understand and didn't get any real answers.
How did I go from being his whole world to nothing?
I caved and sent him a text on Friday after 8 days NC just telling him I missed him and it hurt that I'm now nothing and he is living out our dreams with someone else. His response of I miss you too and have been thinking about you and that he's not that happy and not to worry he's not living out our dreams and that he is now stuck and is just going to try to make it work but wished it was me just made me more confused. I can't get a straight answer out of him he can't just say I'm with someone move on, he contradicts everything he says and the mind games kill me, but how many times do I need to hear that he doesn't want me cause if he did he would be with me... Why can't he just say he's happy rather than lay that little seed of hope! And why am I so desperate for they tiny crumb of hope that I look into it do much?!
I just want to be past this point and right now the love and affection he gave me I'm craving so much. I miss him but I don't want to!
I asked him to be with me and work it out after the series of msgs back and forth the day I sent the MSG ( probably about 5 msgs each) he didn't reply to that one, basically it was a bit of an ultimatum, be with me now or never I won't be an option and I'll push my feelings aside and do what he is doing and move on.. No response.. I'm guessing that's probably because he doesn't want to completely cut it as he wants to think I'm a back up but he doesn't want to be with me... But do I really want him or am I just longing for the good feelings times?.. And is it more about that he has moved on.. I don't get any of it. All I know is I don't want to be here in this space I want to not hurt anymore I don't want him to have moved on or be happy I don't want to be nothing to him. I desperately want to understand.
And I'm ashamed of it all.
And I still feel like I'm not enough.
I do want him back.... WHY!