That teacher is pretty screwed up.
As for the boy, you should try to talk to him. I think that very few people meet anyone, at 15, who they're going to have a long-term relationship with, but shyness is something which takes a long time to overcome (to the extent that it can ever be overcome), so you may as well get started on the process. The results may or may not be what you hoped for, but at least you will have done something, rather than doing nothing and going on wondering what might have happened if you hadn't been quite as shy. One way or the other, at least it gets resolved. And if nothing long-term comes of it, that's fine -- any mostly-positive relationship is something which you will fondly remember, any mostly-bad one is something to learn from, so that you do better next time.
And don't worry so much about your autism. You are you, and labels can't change that. If whatever autism you have is not something that's obvious to someone who sees you pretty regularly, then maybe you are serious, shy, not very social, or whatever, but those are neither uniquely autistic or necessarily bad. It was very creepy and wrong that your teacher tried to use it against you. Most people here think that a little autism can be a very positive thing. In my field, computer science, people with AS or HFA are very accepted -- it's quite common among computer scientists, including the very best and brightest. Everyone does best when they do the things that they love, and are worse at things they find boring. Autism makes you more that way than most people, so your weaknesses may bother you, but your strengths may become very powerful. And I bet that you don't even mind the idea of missing out on a career of door-to-door sales.
So don't be ashamed or uncomfortable, love yourself and be proud of who you are. And, hard as it may be, work your way into more interaction with that boy. If you don't, nothing will happen. And whatever you can make happen is better than nothing. At worst, you'll make some mistakes and learn from them.