The cells that we think of as being our cells sometimes go their own way and multiply beyond the control of the systems that normally regulate our bodies; in an animal this is called cancer; if it was a group of people in a human society going their own way beyond the control of the government it would be called rebellion.
A bacterium (or an organelle) is a very complex thing. It has rightly been said that a bacterium is enormously more complex than a star.
Isn't science wonderful!
While all of what we know of organelles, procaryotes, eucaryotes, organisms, mitochondria and chloroplasts is thanks to science, the main question posed by this page, whether we are a single organism or a cooperative of a great many organisms, is a philosophical one. Like so many philosophical questions, it has no right or wrong answer.
And then there are virusesA virus is typically about a thousandth the volume of a bacterium. It cannot be called a living organism because it cannot reproduce; it requires living organisms to reproduce it. A virus is a product of living organisms, it might be considered, in most cases, as being a manifestation of a fault in the design of living organisms.
A harmful virus may be compared to a meme like religion or any other false belief such as the absurd idea that wind turbines cause illness or that underground water can be located with a forked stick. A meme cannot exist without a hosting intelligent organism to reproduce it. Harmful memes, such as the examples above, are like harmful viruses.
Of course there are good memes and
useful viruses too. Some viruses can help protect us from cancers, bacteria and other viruses.
Going furtherThere is a sequence in the above 'things': organelle, procaryote, eucaryote, multicellular organism. If we take this a few steps further we could go to family, tribe, community, to all life on Earth. The members of all these latter groups somewhat dependent on the other members.
Other related pages...
https://courses.lumenlearning.com/biology1/chapter/comparing-prokaryotic-and-eukaryotic-cells/ includes a useful graphic showing the relative sizes of a big range of organisms.