I"ve been close to three people who have chosen to take their lives. I've learned that if they are really determined and they think you may suspect, they will hide all those behaviors, or almost all of them.
The one clue I misinterpreted was when my friend returned a gift we had given him that was quite expensive. Since he often used it at our home, he said he wanted us to keep it there for him to use. Looking back, I believe even in those four months before he took his life, he wanted to make sure the gift got back to us.