This is a tough situation, and I wish I could offer good advice, but issues like this are always delicate. Don't yell or lecture him. He's sensitive enough right now, and he's probably feeling 'stupid' or an emotion similar to that at this time. I would just hold him. Let him know that you are there for him--that you aren't going to yell at him and lecture him. I'm sure he knows that what he attempted was stupid, but for whatever reasons, he thought it was the best solution at the time. Give him time to talk to you. Keep a watchful eye on him, but don't be overbearing. Sadly, if he is serious about suicide, preventing it can be difficult. The best thing for him right now is to know that even if Kaitlyn isn't there with him, that he still has family and friends who love him to death. Literally.
Best of luck, and my prayers go out to him and his recovery.