this is probably the hardest thing after a break up like this. the fear of never ever feeling that way with anyone again. I feel the exact same thing.
And I think in general I totally understand how you feel. I am calm and concentrated on my own stuff too but then everything always reminds me of him. And I feel literal pain in my heart every time I walk past the places we used to walk or make myself the same food we used to make with him and remember how insanely happy I was back then... and it just hurts so badly to think that it will never happen again...
But I know it will just take time. And you will eventually get over him. I think you should work on accepting that maybe it's even true that you won't find such connection ever again. I am trying to do the same. And think about it all with gratefulness. Try to be happy that it even happened instead of crying that it's over. There are tons of people who never in their entire lives feel such things. So even though it was short and it's over and it may even never happen again, try to be grateful that it even happened and accept the fact that it's over.
Breaking up with someone you were so close to is very similar to someone close to you dying, so it's only natural that it takes a long time to deal with the emotions and the healing process is very very difficult.
And I noticed it's even worse when I try to force myself to be happy if all I wanna do is cry about it. Just embrace whatever you feel and let it all out.