Don't try to be a psychologist giving advice. You should only offer support, not express your views on the matter, if the colleague doesn't directly ask you for advice. Ask more generally how he feels and try to be understanding.
Don't ask how you can help. This can be uncomfortable for your colleague. Instead, be proactive and find ways to make his work easier. For example, when you go out for lunch, ask if he wants you to bring him something to eat. When you talk with a business partner, ask if you can arrange something for the colleague as well. These simple gestures will help your colleague and he will not have to feel embarrassed asking you for help.
Even good intentions can hurt. Being optimistic, you probably want to show that things will take a turn for the better, but your colleague can interpret it as trying to downplay his problems. Each person copes with personal problems differently and you should respect your colleague's needs. You should show that you're listening and say that you understand how hard it is. You will show your understanding and, at the same time, remain neutral. The colleague will not feel uncomfortable and be more open.
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Article source Psych Central - the Internet’s largest and oldest website focused on mental health