Firstly, I think it's a positive thing that you don't communicate with him on any level. I've been in a similar situation, and I found that avoiding all contact and communication was absolutely vital. So, that's one positive that I hope you'll continue at. Other than that, though, I think it's incredibly important that you tell someone what's going on. A parent, teacher, possibly the police. What he's doing is completely wrong, and to make matters worse, he's really really scaring you. He can't get away with thinking that's right, or he'll just continue to do it, y'know? He needs to know that this is wrong, you NEED to be left alone and that if he doesn't stop, he can get into a huge amount of trouble. I'm not sure there's much else I can say other than I honestly think someone with more authority needs to know. Someone who can have a firm talk with him, and someone who can stop this. I know it's not the nicest idea - having to tell someone how you're feeling and what he's doing - but it might actually be the only way to get him to stop. You've already tried to deal with it yourself in confronting him and in telling the school administration, but as you can see, it's not gotten you anywhere at all. And seriously, this has gone on long enough. Far too long. If you just tell someone what's going on, there's a huge chance that all this might be stopped, and he won't be there in your nightmares anymore, y'know?
Also, on a side note, you mentioned about getting nightmares and flashbacks from when you were in the relationship and he treated you badly and hurt you. Do you think you'd maybe benefit from talking to someone about that? I mean, if you experienced any form of abuse whilst in that relationship, it can take a long time to come through it and feel better about the whole situation. Sometimes things can be made a little easier if you have a helping hand.
Think you could give it a go?
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it's broken beyond repair. it's in a million little pieces.