I don't believe my friend's friend died.
Why don't you believe your friend's friend died?
I think it's just too suspicious.
It is odd to be skeptical of someone's death and it is hurtful to your friend to disbelieve their loss happened. Instead of being doubtful you should be supportive. Do you have a reason to doubt?
I just want to be sure before I believe it, You never know.
Your friend is likely going through a difficult time. Acting as if he is faking it is just insulting. Try being there for them instead and supportive.