must say that your post has many resemblances with how I've been feeling lately.
When I came here one and half year ago I didn't know what exactly I was looking for except that I felt so lonely and like stuck isolated from outside world while I was intensively traveling because of my work.
It didn't pass long and I started therapy trough which I learned about some my inner struggles that could be explained like feelings of extreme and anxious isolation from outside world, it is very lonely place that I've been caught usually in early mornings just before I would wake.
It is like some big hole is in me that can't be fulfilled no matter on any try. I've never before felt it is so intensively. As you said it is like something big is missing from my life and particularly from my childhood and I was occasionally sad when I think about it. During last Christmas while I was shopping presents for some nephews I bought one Teddy bear for myself. At first I didn't know what to do with it, than I put it on my bed and it wasn't long before I started to hug him when I would felt lonely in my bed. Even I'm surrounded with many friends, and even I have had girlfriend back than nothing could prevent showing of those feelings.
In therapy I've already been talking with my therapist about isolation and we just have decided to tackle it directly.
I've had birthday on last Saturday and I went out with couple of my friends and had great time, but next day I've been caught feeling like trapped and completely alone again.
I felt like some huge hammer is hitting through wall bringing those negative feelings back.
One good buddy told me it is evidence of process that started in me.
When it starts everything looks like seen trough some microscope.
I felt like that for a while and I was wondering about it. Ever since I started dealing with my issues I became more sensitive on some things that I considered already as "problematic" and some even become more difficult to handle.
I'm not sure for how long it will last. Certainly this empty hole has built for long time and time will be needed to fill it.
But I learned that every single little steps counts.
So in that respect I admire your reaching out trough writing and discussing your pain, you are acknowledging your true feelings even they are hurtful and you are connecting to inner self. Above all you are ready and brave enough to share it with us.
That is healing!
You are not alone