Grammar question, please help, thank you?

No, the comma is unacceptable in both of those places. It should just be written like this:

(1)
I don't like Tom because he is selfish.

(2)
I met the boy who saved my life.

No comma needed in the first one because 'because' is a joining word.

The second one doesn't need a comma either.

1 needs a comma because the "because he is selfish" is not needed to make the sentence dependent and it doesnt change the meaning of the sentence. So yes it needs a comma.
2 does not need a comma becuase "who saved my life" is needed for the sentence. "i met the boy" means something different with "who saved my life" at the end. you are meeting a particular boy therefore you need it so NO comma! (: hope i helped!!

(1) needs the comma(2)doesnot.im positive! :) because try putting the clauses(what came after comma)at the beginning of sentence...the first one makes sense at the front so u put the comma there..the second makes no sense in the front

1) I don't like Tom, because he is selfish.
You're saying that you don't like Tom, and explaining because he is selfish therefore, the comma.

2) I met the boy who saved my life.
You met the boy who saved your life. There is no pause in the sentence and you aren't following with a conditional because you met the boy. They are all acceptable sentences except "I met the boy, who saved my life." There's just no reason to have a comma there.

The first one needs a comma. The second sentence doesn't.