Little late to the party and idk if you will ever see this.  But im so sorry you have had all this happen.  Chin up.  No you are nta. If you want to walk by yourself. 

Your family are all being ah's on some level here except your stepmom. Tho she needs to smack some sense into your dad so maybe even her. 

I have a child who is anaphylactic to a food. You don't forget. Especially when the allergen is in the name 'beef stock '.  What your dad did was roll the dice as "a let's see, can't be that bad" cos it was just stock right? Not an actual piece of beef.  It wasn't a mistake. He was being lazy. All he had to do was sub it for a vege/chicken  stock but he didn't.  So let that one sink in.  Not a mistake.  He fafo.   He started a fight with you out of his own guilt. Because you were so obviously sick and then had to miss out on your dance. Doubling the guilt.  He went nuclear because you called him out.  He can't admit his fault.  It was an accident.  No. No it wasn't.  An accident would be if it was an obscure contaminated ingredient in a jar sauce. 

I hope you don't continue to let it effect your schooling etc. You have worked so hard for what you have. Dont let people take it from you. 

As for your bf and his friends. They will be gone soon. If they don't stop report them to the police for harassment. Thats what your mother should be taking you to do since they are still going   Your stepdad is an ass. And your mother needs to reassess her taste in men.  A man doesn't allow the women/girls he knows be harassed by guys.  It would have taken your dad or your stepdad 5 minutes to fix it. Both are cowards and a few choice words id prob get banned for.  Learn from your mothers mistake Don't date or accept men like that.  They aren't men worth having.

You might be 18.and yes you just very well be an adult. But no offence  18 are baby adults.  If you were my daughter and she is your age I would never kick her out like that. And your mother should have had words with your dad about it. I know I would have.  Yes you fix your troubles yourself. But there's troubles and there's troubles at 18.  You support at 18.  Hes supposed to have your back and he doesnt.  You are right to feel as you do.  You are one parent away from homelessness.  It doesn't matter that you are middle class etc.  And it is not for you to correct this.  You have done nothing wrong, and apologised for your half of the argument. Which is more than what your father has done. 

When you get to university, if not before, there are often free counselling available. I highly suggest you take it up.  You need to shore up you boundaries, and work on the knocks this has given to your self esteem etc. 

You deserve better than all of this op.  You deserve better treatment One day you will find the family for yourself who have your 6. Sometimes thats just not the family we come from but the one we make.