Going back over 20 years now but my brother in law who was also my best mate at the time had split from his partner, he went through a really rough time and had us all worried. Anyway I called in to see him after work one night as I was concerned about him and was really happy to find him in good spirits and the best I had seen him for week's. It turned out that he had met someone else and really hit it off, we had a good chat and spent the next few hours having a good laugh, I left safe in the knowledge that he seemed to be over the worst.
14 hours later his brother called to say that he had hung himself, I would have never guessed this was on his mind when I left and spent a long time wondering why I didn't pick up any signs.
It's a horrible thing to go through and please don't attach any blame or guilt to yourself, you don;t ever know what internal demons people are fighting.