This is really a case of restrictive/non-restrictive phrases. "My friend Tom" is restrictive, so don't use a comma; "My boss, Mr. Andrews" is non-restrictive, so use a comma.
1. I found out from my friend, Tom. = I am talking to "Tom." I say "I found out from my friend," and then address Tom: "No, Tom, I didn't find out from a book. I found out from my friend."
1a. I found out from my friend Tom. = I found something out. The person from whom I found this out is my friend. This particular friend is named Tom. Out of all your friends, we're talking about the one named Tom. This is a restrictive phrase.
2. works because you only have one boss, so his name is not restrictive.