Little Jay, I'm sorry you had this bad experience and hope you won't generalize it into thinking it's always wrong to open up. I would encourage you to think about what you wanted from him.
Support, understanding, compassion?
It sounds like he panicked and didn't know what to do except to blurt out you needed help and should go back to the hospital. Now, why would he do that? Probably because he was afraid, afraid something bad might happen to you. Maybe his first priority is that you stay alive, that you be safe and get into a frame of mind where you feel better about yourself.
Is that so bad? Is it really so terrible that he wants you to be safe? And the thought of you being unsafe in any way at all scares the living bejaysus out of him?
Maybe he's just an inexperienced guy who doesn't know what to do and in his panicked state, all he could think of was how important it was for you to be safe.
All of that is the long way around of saying that if we want compassion and understanding and support from other people we're far more likely to get it if we can give it to them in return. Can you understand why his first priority might be your safety? Can you show compassion for his fear and panic and his inability to know the "right" thing to say? Can you offer him support even though his reaction disappointed you and left you reeling yourself?
I've been reading posts by you in other forums, Jay, and I know you're going through a difficult time right now with lots of sui thoughts. It's a time when a person needs the love and support of their friends. Even though you're in pain, can you show your boyfriend some of the compassion in your heart so he can begin to feel safe supporting you? If all you show him is anger and hurt, he will feel pushed away and more panicked himself. It may be hard to believe, but giving compassion and understanding is really the best way to get it in return.
He blew it, he panicked, he said the wrong things.
Can you open your heart and forgive him for his blunder? If you can, then maybe the two of you can face this crisis together. If you reject him because, in his inexperience, he didn't know the right things to say and do, it almost guarantees things will only get worse. I wish you the best, Jay. I know this is very hard for you. I'll be thinking about you and hoping your T and Pdoc will be there to help as you struggle to find your way.