(XO) Ohh, don't you forget
(XO) Don't you worry 'bout a thing
(XO) We'll be everything you need, just believe
(XO) Yea, (XO) whoa

from The Weeknd – XO/The Host Lyrics on Rap Genius

Meaning

XO is The Weeknd’s clique.
XO is a drug (ecstasy and oxycodone). He’s saying that him and the pills will be everything she needs. Or that him and his XO entourage will be everything she needs.

Also, the crew’s name being XO has a lot to do with hard liquor. As pictured earlier in the explanation. Hennesey XO, Patron XO. Etc.

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