Why do you feel such a need to tell your friend? I think broadcasting one's suicidal thoughts is at best selfish and at worst malicious. It drags the person you tell into a terrible situation that they don't deserve. I don't begrudge my 'happy' friends' happiness and I absolutely don't want them to fret over my impending demise or feel obligated to take well-intentioned but futile steps to intervene. I know suicidal is a very lonely place but I think just talking about the things that make you feel this way is as constructive as the conversation is going to get.