lover vs fellow

lover and fellow both are nouns.

Word	Noun	Adjective	Verb	Adverb
lover	Yes	No	No	No
fellow	Yes	No	No	No

As nouns, fellow is a hyponym of lover; that is, fellow is a word with a more specific, narrower meaning than lover:

lover (noun)	fellow (noun)
a person who loves someone or is loved by someone	a boy or man
an ardent follower and admirer	a man who is the lover of a man or woman
a significant other to whom you are not related by marriage	a friend who is frequently in the company of another
	a person who is member of one's class or profession
	an informal form of address for a man
	a member of a learned society
	one of a pair