My boyfriend tried to kill himself...

My boyfriend and I are both 15 and he has been having symptoms of depression for the last 3 months or so, but lately it's been getting a hell of a lot worse. He told me that last night he almost killed himself by choking himself to death with a belt, but stopped last minute because he wasn't sure if he truly wanted to leave me and die. I'm so stressed and worried about him. I got him to go see the school counsellor last week, and he said it went pretty well. I want to see if I can organise for once a week now. He's an introvert and doesn't talk to anyone about this beside me. What should I do? I feel so lost and I CAN NOT lose him. Please help!😖😖😖