yes, a harem can mean multiple people being attached to a single person, it can be affection, adoration, love, worship, etc.
usually, harem is used for when a male has multiple females attracted to him, and reverse harem is when a female has multiple males around her
but people also loosely use the word for basically a group of people attached to one person, even if it's only by respect/camaraderie even, esp. in shipping community
in intercourse terms, you'd usually encounter gangbang, orgy, 3p, 4p, 5p and so on to refer to multiple people doing it as a group.
or the word "poly" is attached in front of a word, which can mean they are in a relationship with multiple people, may it be romantic, sexual, and so on

as someone who has read the whole novel, here's some big spoilers:
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dw, it's a happy ending.
although our mc ends up with ml, he gets a super devoted team (basically harem) who'll prioritize mc over everything (and i mean everything)
he also only does the snu-snu/smex/papapa with our ml
if i were to describe it, it felt like fluff horror tbh, dont worry too much