Ok, first off!

Re-read your post and pretend it isn't you, ok? (Yeah, that's tricky). If you're in any way successful with that pretending... you'll notice a few things in here about yourself.

1. you're blaming yourself way, way, too much - It is OK to break up with someone! It truly is, and it's kinder to break up with someone early instead of leading them on. You did NOTHING WRONG.
2. You have continued to punish yourself for this, INCLUDING accepting any bulls*** he's thrown at you since.
3. Priorities are necessary - right now your priority is school. There is nothing wrong with that!
3. He is manipulating you, whether or not he intends to. He intentionally guilt-tripped you when he said that friends need to talk regularly - No, actually, they don't! I don't get to talk to some of my friends for months and we are STILL very good friends.
4. He has ignored your requests for space and he has clearly ignored your emotions (as shown through his lack of acknowledgement of your confession)
5. You do NOT "owe" anyone a friendship. Do you owe him sex? No. So would you owe him friendship? No.
6. It is not karma.
7. "my self-esteem got blown to bits when I heard he found someone else and he still wants to be friends". Absolutely valid feelings! This is what a councellor could help you with. Have you questioned why he wants to be friends now that he's in a relationship? There is a chance that he's genuine, but there is also a chance that he just wants to make you feel jealous and hurt. That, or he's unhappy in the relationship and is using you for an emotional ego-boost. Any of those could be true.
8. You're way of dealing with this stuff has been to let yourself get used by him and to not at ANY moment consider your own happiness or well-being. That isn't dealing with the situation! That's letting yourself get used, and making yourself miserable! It's not dealing with it at all
9. "I'm dealing with what an adolescent student deals with" - you've just completely trivialized yourself and your entire experience. This signals to me that you reallllly have a low self-worth and that a councellor would be REALLY REALLY BENEFICIAL. This line makes me worry for you, because your issues should not be trivialized in that way. They're a real and genuine issue; people have trouble moving on at all ages. People allow themselves to get used at all ages. People need help with self-esteem at all ages.

Can you see how that is true?

Your ex sounds like a really poisonous presence in your life, and it does not sound at all like you need him complicating your life.

It's ok to need or want some help you know. You've got a lot on your plate!

Have you explained to him that you NEED to concentrate on your education right now and that you just cannot afford the time he seems to expect of you? Make your boundaries clear and ENFORCE them (this is if you aren't willing/able to just do a clean cut)