If he really is a black belt in Tae Kwon do, then he absolutely should be able to kick your butt without much trouble at all.
Decent Tae Kwon do schools teach their students to walk away from a fight if they can, so actually it's likely he's violating the teachings. If not, then the association his school belongs to should be having something to say about this student's behaviour.
However if you're determined to get him and just won't let it go, then he is allowed to defend himself against your hostility.
You wouldn't be picking on him or his friends because they're a year younger than you right?
If you're acting as a perpetrator then he is 100% within his rights to take action.
Let me ask you this though. What if you sidestep, slam him in the head, he loses balance, falls hard upon the concrete and dies?
Will you be up for manslaughter?
The answer is either possibly or probably, depending on the circumstances.
If you both conduct this fight at school and are caught, will you be suspended or even expelled?
What if one of you breaks the other's rib and that rib punctures a lung?
It's a horrible death to slowly suffocate on your own blood.
Anyhow, the #1 rule of fighting is that you only do so if necessary. It sounds like this situation is orchestrated and mates on both sides are revving you both up. That's how it typically goes. Your friends get some excitement for the day in their own personal little piece of bloodsport, but you have to take all the risks. You could be permanently injured, perhaps even die. In that scenario you lost. You could do the same to your opponent, so you win, but then you face legal consequences.
In truth you only win if you beat your opponent without injuring him and he surrenders. However since he's a black belt, I still think he will kick your butt.
Overall, you're better off working this out together if you can. Your mates don't want you guys to get along because they desire excitement for the afternoon, butt they're not the ones risking all.
Work things out if possible. It's the best move you can make.