Torn in between

I miss them.
I felt incomplete with him without them.
This is my failure to grasp what happiness is.
Ironically, I really don't feel that happy.
The heart that had once opened up is now closing up. There is just no sparks or feeling that I think I can be open with him on everything.
The more I know him, the more I think we are not for each other.
It seems he still doesnt get me for what I do despite knowing most of my background. 
I just realised at this instance that although "he" doesn't know me more, we could still communicate very well and very comfortably together.
Why?
Is this called chemistry?
I know feelings are unreliable.  He is more reliable than them. But I feel bad I have not been able to bring myself to put in effort to show my care and concern more to him.
My mind is constantly preoccupied with work and studies.
Moreover, I really feel we have too many disagreements in many areas.
Wedding, behavior, mindset.
Perhaps I accepted too quickly.
I don't know why. He is deemed as the balance between the two. But I really cant find the balanced point.