The suicide of a colleague can have a profound emotional effect in the workplace, and it's important for you and your co-workers to support each other. Some people may struggle with guilt and unanswered questions about what happened and what more they could have done to help.
Consider talking with a counsellor to help you cope with the suicide. Your employer is likely to provide counselling through your company's Employee Assistance Program (EAP). If not, speak to your GP to get a referral or call the beyondblue Support Service for information about mental health professionals in your local area.