Why is this happening?

My opinion on bad experiences is that they exist to make us stronger, and, I suppose, weed out the weak if you want to be morbid about it.
Every negative experience you have gives you tools to use in the next one, whether or not you realise it, and we all have bad experiences, they come and go like the weather, part of a bigger system.
Another thing is to try and keep it in perspective, I realise that you feel like you have been bullied and that it is unjust, but what brought it on? Does this person have stuff going on in their own life that may have prompted them to take out their emotions on you? Could you have helped them with that instead of feeling victimised? Being honest with yourself, were you being truly bullied, or just reacting strongly to something negative because you've been made sensitive by past experiences?
Finally, in the grander scheme of things, is what this person did to you really worth the time and effort you are spending getting back at them? Or is there somewhere better you could focus your energy to achieve better results for yourself and the world around you in general? Sometimes the universe denies us things because we're fixated on something small, rather than seeing the bigger context and the lesson that surrounds it :)

I would suggest not forgetting the three-fold law and looking it over in other forums on this site. And thinking everything over would also be a good idea (as a few others were saying).

Keep in mind, the three fold law isn't believed by all faiths, and not every magic user believes in it. Although I think I can see where you are coming from.

Why would I do something to make someone bully me. I didn't. Why would I do something to someone rape me and why would I do something to make someone kill someone close to me?