I know. I understand, I really do. And I feel for you, here you are wondering if you're going mad, so you go onto MN and here we all are bombarding you with information about what is actually a serious personality disorder. It's a lot to take in.
But you know we are right - most of us have first hand experience and we are all predicting what he will do. And now you know, it's kind of academic what you used to think - that's the past now.
Now, in the present, it's time to put your big girl pants on and just fucking do it - just tell him to go. Because now you know you can't un - know can you?
Otherwise not only is this going to keep making you feel shit, you will feel doubly shit because you knew what was going on and didn't do anything! It adds another layer to it and changes it into a situation you need to change urgently,
That will be an even more shit feeling, trust me. He's an animal in a cage (actually I love animals and it's a terrible analogy). He is what he is and will be what he is forever. You're the only one capable of change here.
You are literally the only human being here with free will. He will keep biting and biting and biting.
When I was little my parents took me to a zoo of some sort. There was a cafe with a ferret, or weasel in in and big signs saying not to put your hand in, it bites. What did I do age 3? No prizes for guessing. You are not 3.
The damage you will do to yourself and your belief in yourself will be even worse than his shit if you stay. He can't help himself but you can.. and when we are at a low ebb and make low ebb decisions that have ongoing repercussions it makes us feel even worse.
It's bloody hard, but not as hard as digging yourself out of the depression and self blame a year down the line, and the good side is that if you do this we will still be here, and you will feel amazing, and in control. In between mourning the loss of what you thought you had but didn't.
It's bloody hard, that part. But what can you do? Staying isn't an option is it? He won't dump you. If you let it drag in by the tine you get to uni you'll be a mess.