Literally I would just type he/she is my ex and harasses me. Please move me to a different seat as I've requested because I don't feel comfortable and should not be subjected to harassment in your classroom. Then copy it and just hold down paste on that shit until it gets about 20 pages long and hand it in. Then walk my ass to the principle's office.

I would write the following: "The person sitting next to me is my ex. They haven't stopped harassing me since the break-up. And I do NOT want to be sitting next to them. Period! Thank you in advance..." And write it big enough that it takes 3 pages.

go over your teacher's head. in fact, you should probably be reporting the harassment.

Just wrote a three page list of the things your ex has done. The more details you can add, the longer your essay will be. And if all else fails, go over the teacher's head. Principal has to listen to your problems and at least appear to take action.

If it's really that important to you then stop being lazy and were the essay. It's not hard to fill 3 pages with personal experience and you can even double space it if needed.

Page 1 I Page 2 hate Page 3 my ex

You need to report the harassment to someone higher in the chain of command now, before it escalates. Now you should also report the teacher for failing to properly handle harassment in the classroom. Especially since I think schools are supposed to have regulations and that there are laws in most states stating that the school, all staff and all affiliates are required to provide a non-hostile and relatively comfortable teaching environment to all students. I'm also pretty sure that part of fair treatment of students is that it means that making a student write an essay-because the teacher doesn't understand what being harassed is like, goes against regulations and school rules. So, report the harassment and improper handling of the case to the principal, or whoever is directly above the teacher. If there's no action, go up the chain, even to the superintendent of schools and school board. If they don't want to handle it, go public. I suggest getting together a sort of time line to present to the principal. When the harassment started, when and why the relationship (when there was one) degraded to the point of a break up, types of harassment and when they occurred, responses by other student and by teachers to the harassment. I'd say to get evidence of them in the act but that could cause trouble for OP. Unless the class is predominantly lectures, and OP just so happened to be using a tape recorder before the ex starts harassing them... To say again, go up the chain of command; report both the teacher and the ex. Going over someone's head /can/ cause issues down the line, but if you keep record of when you reported them and got copies of your transcript as it stands now, you should be able to prove any unfair grading that may occur.

Do the essay...it'll prove your will and how badly you want it done

Well you could just repeat "He is my ex" over and over, and if that doesn't work, go to the principal, and if all else fails, eat pizza, all problems are solved with pizza.

You have good reason for not wanting to sit next to him, so write the essay and slay that shit