I went through this stage and tbh a lot of people do. I'm doing Psychology at Uni and in one of my module exams in January I got an E. I re-took it in June and bumped it up to an A.
You can do it if you work for it. I wasn't willing to throw my future away and spent every minute of my free time speaking to my teachers and going to extra classes to prove to myself and them I could do it. I know exactly what you're feeling hon and my friends all went through the same. The feeling's awful but you've just got to keep plodding along at it.
About the relationship thing, I was the last person of my friends to have my first kiss and have sex. I was 16 and 18. And it didn’t bother so at all so it wasn’t really an issue for me not having a boyfriend and not being in a relationship. I didn’t feel uncomfortable seeing my friends with them. You’ll get over this boy honey, I’m sure J
Everyone’s worried about leaving their friends behind but you’re going to have to do it sooner or later. And at Uni you’ll more than likely meet some of the best people in the world.
Keep your chin up dude! It will get better.