late 14c., past-participle adjective from obsolete verb belove "to please; be pleased with" (c. 1200), from be- + loven "to love" (see love (v.)). Noun meaning "one who is beloved" is from 1520s, first in Biblical language.
word-forming element of verbs and nouns from verbs, with a wide range of meaning: "about, around; thoroughly, completely; to make, cause, seem; to provide with; at, on, to, for;" from Old English be- "about, around, on all sides" (the unstressed form of bi "by;" see by (prep.)). The form has remained by- in stressed positions and in some more modern formations (bylaw, bygones, bystander).
The Old English prefix also was used to make transitive verbs and as a privative prefix (as in behead). The sense "on all sides, all about" naturally grew to include intensive uses (as in bespatter "spatter about," therefore "spatter very much," besprinkle, etc.). Be- also can be causative, or have just about any sense required. The prefix was productive 16c.-17c. in forming useful words, many of which have not survived, such as bethwack "to thrash soundly" (1550s) and betongue "to assail in speech, to scold" (1630s).
Old English lufian "to feel love for, cherish, show love to; delight in, approve," from Proto-Germanic *lubojanan (source also of Old High German lubon, German lieben), a verb from the root of love (n.). Weakened sense of "like" attested by c. 1200. Intransitive sense "be in love, have a passionate attachment" is from mid-13c. To love (someone) up "make out with" is from 1921. To love and leave is from 1885.