I can relate to your feeling " Alone in a Crowd"
There are a lot of people who look toward Spiritual groups or self help type discussion groups for this reason.

I personally have met MANY people who say that.
"They never felt they belonged" No matter how many friends, they have or even how succesfull they become !

It's is also described as an emptyness or hole (in the gut)

Also, most people who suffer or recover from various addictions describe the same feelings and that only through belief in a higher power is the stress reduced (Not removed) just reduced.

I am 57 and have met and known hundreds of people personally with these feelings. So, you are not alone

PS when i speak of Spirituality I am NOT speaking of religion !

Reach out and keep looking for a group of like minded people.

12 step programs are great and ACOA Adult Children of Alcoholics is
also an excellent group if there is or has been addiction in your family !

Hope this gives you somewhere to look

"A New Earth" By Eckhart Tolle is also an excellent book to help us understand ourselves !