Hey man! First off, my PM box is always open. Please reach out if you need anything. Second, I'm not a doctor. Third, you put a lot here. I'm gonna TL DR if you're short on time.
Please go find some help. If you don't feel comfortable with psychiatry, go find someone to talk to. Getting this off your chest to someone will not only help you work through it, but will give you the chance to see you can have normal conversations about things you are passionate about. A great therapist is something that needs to be found; psychiatry as well. Find people who aren't part of your life who you can get these thoughts out to. Please don't do what many people in this country do and wait until they break.
Let me tell you a little about me. I have taken low-level meds since I was 13 (specifically Bupoprin (Welbutrin)), to increase my energy. As a kid, I was sleeping all the time and I had zero friends, but it didn't affect me. In college, around the age of 20, I had my first episode of mania; where I did some impulsive things, did some great things, but at the expense of losing my mind and my sleep. I sought help six months later and found out the severity of my disorder.
So I started medicating. Prescribed and self. But self medicating necessarily put me into contact with other people, and I learned a lot of shit. For example, in conversation, try to get the other person talking about their passions. It becomes so much easier to talk when you can get the other person to start yapping. Ya, this doesn't work in large groups, but it works in small ones. Sure, the weed helped people open up and, for me, reduces paranoia. But the idea is there.
You've started your own clothing line? Besides Kanye, I can't name anyone else who's done that. And guess what? That's okay. Genuine people will be interested in something they do not know; just like you might find interesting snowboarding or audio production or kayaking.
But I think there's a bigger issue here, fellow INFP. A few days ago I was "encouraged" (read: required) to go to a happy hour. I knew the people who would be there and couldn't stand them. They were terrible people, we had nothing in common and it would be awkward. I showed up for 5 minutes, freaked out and left. On my drive home, I realized how stupid it was to feel so alone when there are people, not necessarily my best friends, but who've invited me to a bar and just want to talk.
The best way to get out of this funk you're in will be getting out of your comfort zone. It is probably going to get worse before it gets better. But guess what? You'll gain life skills that will carry you to your success, even in your clothing line. You'll learn that everyone is different, which means any one person you talk to can help you; usually not directly, but they know someone who can help. I've read a lot, but I've never read the book you're referring to. Try reading "Never Eat Alone" or Gladwell's "The Tipping Point."
But, chances are you won't find these amazing people right of the bat. There will be awkward silence. You will say "Look my drinks empty" and hope that the other guy doesn't notice its full, or it will happen the other way around. Guess what? You're not best friends with 99.9% of the people you meet. It's a numbers game: you've just gotta find one person who you connect to, and you will increase your probability the more you get yourself out there.
You are an INFP. Being around people all day will exhaust you. But that doesn't mean you can't be outgoing and you can't go out there and make friends. I mentioned I have trouble with paranoia, and it was very hard for me to trust, let alone talk, to others. In college I decided I wasn't going to be a recluse: I talked to people in my classes. When I realized I couldn't stand them, I volunteered for a dog shelter. Dogs are great. Then I met this guy who knew my Orientation leader. I got involved in a Fraternity. (Your school might still be living under the old philosophy for Greeks, but there are organizations out there focused on making better men/women. Find them, it's not animal house anymore, and really helped me grow as a person by forcing me to be around and meet others). Then I was able to gain the courage to go to the college radio station and say it was something I really wanted to do, and we were able to work out a situation where I became an underwriter, than a DJ, then a Director on the executive board.
I'm not writing this to brag; I'm writing it to tell you that if you want a different outcome you have to do something different. It will be uncomfortable. You will talk to people and the conversation just won't be there. How much have you dated? This is the exact philosophy behind any kind of dating; talk to someone who seems interesting, and if it's not there, make an excuse and try again. Sometimes someone will dismiss you, and that's okay. You know that not everyone meshes.
Just do me a favor and don't lock yourself in your room, and don't stop following your passion. Find things that interest you. Maybe your city has a meetup group for fashion designers. Go. There you know you can talk about your work, and you'll learn something and might find a professional mentor, or if you're lucky, a personal friend as well. Pick up hobbies; find people at your university who have those hobbies. If there's not, start a club. At my undergrad, we could create a club with 5 signatures.
TLDR - You're in a slump, and that's okay. Priority 1 -- Go get help, or at least someone outside of your life who will talk real with you. We don't have your entire story, and more importantly, this could be chemical. Please seek help. Also don't stop following your passions. If one of your dreams is to regain your confidence, you're going to have to leave your comfort zone. Find people who have your interests; it will be easier to talk to them. Find people who don't share as many of your interests, and practice getting them to talk (Quick tip, just repeat the last few words they've said as a question if you want them to keep going). Maybe you'll find something in common, but more importantly you'll get practice talking to someone. You'll get through this, it will get better, but you've gotta get out of your comfort zone and do some different things if you want your life to be different.**
Good luck, stay well, and remember you've got a friend in me here. My PMs are open.