I'm a older than you (like 20 years!) and I think it's great that you've got some help so young so that you can start working on your goals & get what you want out of your social life & relationships in the future. Some people find a diagnosis helpful so they can pinpoint their goals & achieve them, some people find a diagnosis unhelpful due to stigma. I found it helpful to admit that I was avoidant, accept that I was avoidant and so cancel out other explanations for my suffering & loneliness, that way I could target ways to participate socially more & better understand myself.
Regarding relationships, of course you can have them. I've had long term bf's. Once the relationship was underway (say, the 2nd or 3rd date) my avoidance didn't have anything to do with the relationship, not the problem. It was only that first stage of getting to the first date or getting that first date to happen (for example you, have to actually socialise in the first place to meet someone new who you want to go an a date with! then you have to figure out how to talk to them without turning beetroot or tripping over a chair, how to ask someone on a date or get asked on a date).
I agree that exposure therapy is very helpful. I've done tonnes. I started by walking down the street trying to make eye contact with as many people as I could and gradually built up from there. At your age I also started getting out of my comfort zone, by my mid 20's I leapt head-on into my fears e.g. travelling overseas by myself; teaching at work - having to get up in front of a class of students & talk! both were so hard but made a big difference, when I was younger than you I struggled even with into a shop & buying bubble-gum, so I've come a long way.
Anxiety is a huge underlying cause of my avoidance. So any methods that can help you lower or manage your anxiety is critical, I think. Lots of people find breathing or relaxation techniques helpful. I had to try different things before I found what helped. I think it's very important if you're working w a counsellor/psychologist to trust them & feel you're making progress with them after a certain time.
I joined two avoidance support groups (in real life). The people in their 20''s were optimistic, goal-oriented, positive. I enjoyed their company. In contrast, the people in their 40's and 50's were depressed (another whole mental illness on top of the avoidance/anxiety), deeply negative with no goals or much hope for the future. I found it hard to be in their company. From that experience, I thought it's waaaaay better to start working on avoidance young, if you let it get the better of you if seems to drag you into depression. Just my 2c.
hope this helps some, let us know how you're going
