He told her pretty much everything. From what happened during his childhood, and what happened a week ago. This was the first time he actually wanted to tell someone about it, because his therapist was out of his control. Of course, he had the choice not to talk about it with her, but he was already at the hospital and everyone there knew what he did. No point in hiding it.
This was different for him.
Isabelle heard everything he had to say, and couldn't avoid those treacherous tears that fell during his monologue. She knew he had hardships, but she didn't expect something like that. Him trying to end his own life at barely nine years old, fighting with those thoughts throughout his life, and now relapsing again.