HI 'He' is certainly the subject, but 'who' or 'whom' refer to Emma, who is the object of the speaker's belief In English, 'whom' is falling out of use. Strictly, you should use it if the person is the object, rather than the subject ... - I love Emma, who is wonderful - I love Emma, whom I met last year But, to be honest, very few native speakers use 'whom' like this now.
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dave_anonPeople almost always say 'who', in any contextI am one of the people on whom you can count to differentiate between who and whom in formal writing, if not daily speech. It's just who I am.