How to find friends? Looking for social advice..

Hi
You know how it is with porn use. You are more focused on digital world than real..
Well, I am 20 years old now and after my GF I have nobody else to meet, or talk to. Well I have a 25 years old cousin and 30-some years old female cousin. But they are basically strangers for me, they are absent from my life. I dont have any brother/sister. And before you ask, there is nobody here to start relationship. Also, no those stereotypical old friends from school that I can meet up. I havent formed any strong relationship in my puberty and highschool period.
I live in small town. Generally old people live here. Nothing interesting here, except swimming pool and the woods where I can exercise.
I even have 30 km to nearby gym..

My days are spent at home. I try to distract myself with books and exercising and meetings with GF. But I feel sometimes soo isolated. This boredom just makes me feel more urges.

Like fuck, sometimes at University, around peers I feel like a dinosaur that just left the cave xD :/ When I meet someone, after few days of our "relationship" that person goes to his/her friend. I realised that everyone in my group already found that one person or group which he keeps with. You know what I mean, and I still have nobody like that. After one year. So I always try to mindle or stay alone.
Sometimes in a group, even if I try I am ignored by everyone, that quiet unspoken "Just leave us, we have fun you dont belong here"
I also dont want to start conversation with anyone, I dont feel like it. I am just anxious sometimes. Because social anxiety is my biggest struggle currently. Damn.

Sometimes I am like "How these people do it? Its only few weeks and they already know each other very well, as if they already knew themselves before going here"
Seems familiar to someone?

Any ideas? How to change that ? ;/ I feel stucked. I feel like there is no option for me to meet someone new. And I am confused, what I am doing wrong?