Why did my brothers friend kill himself when he had friends and was a popular guy?

Sometimes the people that seem the happiest to us are the one's that are the saddest inside. They will try to seem happy so nobody knows the pain they're feeling inside. I know this because this is how I act sometimes when I'm very sad. People would never know it. But then I heard this guy say to a friend once yeah people that always seem happy are the ones that kill themselves. Some people are upfront with their unhappiness and wanting to kill themselves and others lock it deep inside. My guess is this guy even though everything looked great on the outside, nothing looked good on the inside. You never really know what's going on inside of someone's mind unless they talk about it. I'm very sorry for such a horrible loss of such a wonderful person. All we can do is pray he's happy now and is with God in heaven. God bless you for caring so much! His life lives on in your memories and in the people who loved him. Your brother may just be handling it his own way. Sorry to hear about such a tragic loss!