boyfriend vs lover

boyfriend and lover both are nouns.

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

As nouns, lover is a hypernym of boyfriend; that is, lover is a word with a broader meaning than boyfriend:

Other hypernyms of boyfriend include adult male, man.

boyfriend (noun)	lover (noun)
a man who is the lover of a man or woman	a person who loves someone or is loved by someone
	an ardent follower and admirer
	a significant other to whom you are not related by marriage