Larry & The Negative Spirit and Shipping: Question - Is shipping with Larry polyamorous by default? The Negative Spirit is always there and it loves to interfere so at the very least it's a sort of unrequested wingman if not more. It would definitely help them on dates by projecting them into each other's minds so they could have a dream date where Larry doesn't have to be in his bandages. It did that for Larry and John when John was dying. Honestly a third partner would probably be accurate for it, although an unconventional one.
Larry & The Negative Spirit as Parts of Each Other: Their relationship is complicated. They're one but they're not. It's almost the personification of what makes Larry "different" from everyone around him, and he kind of resents it for that (his self-loathing extends to it) but the more he accepts himself the easier their relationship becomes and its main goal is to get Larry to love and accept himself (and other people) and in that way his relationship with the Negative Spirit is like a metaphor for, at first self-hatred, then self-acceptance and self-love (both getting over his severe internalized homophobia and accepting his disabilities).
Larry/The Negative Spirit as a pseudo-romantic relationship: But it's also played a lot like a romantic relationship. A flawed but deep one. They're separate entities. They fight like an old married couple. They are terrible at communicating with each other. They love each other, they hate each other, they're stuck together, they always come back for each other. They're a part of each other. His relationship with the Negative Spirit is the only relationship he's had that he tells John about when John asked him if he had been with anyone else since they were together when they were reunited. Larry and the Negative Spirit actually have a baby together (and it leaves him which honestly is rude of it).
The Negative Spirit on labels (names, pronouns, species, etc.): Larry "give it a name" as the first thing he thinks of for the alien parasite he just threw up Trainor never gave the Negative Spirit a name. He actually didn't name Keeg either (Larry and the Negative Spirit's son) a sentient cloud of mist read Keeg's mind and told Larry the name - I don't know whether Keeg based his name on the dream Larry had where Cliff was talking to Keeg in larval form and said "keegaboo" instead of "peekaboo" or if it always knew its name was Keeg/named itself that super early on and that being in the dream was him trying to communicate that. In the comics there is only one Spirit and its name is Keeg Bovo but in the show The Negative Spirit and Keeg are different entities (unless the Negative Spirit was like... reborn in Larry as Keeg, which is definitely not how Larry sees the situation but honestly we know nothing about them so it's possible). I think Larry's "give it a name" attitude toward Keeg shows a lot of character growth for how much more accepting he is toward the Negative Spirit (and all it represents) compared to the 60 years he spent fighting with the first Negative Spirit.
He calls it "pal" and "buddy" and the Negative Spirit will see those as its name as much as it sees "The Negative Spirit" as its name (Negative Spirit is also the name of its species). There are other words Larry has used for it, but it can feel the intentions behind it, and those are the only ones that feel close to the concept of a name. It can feel the malice behind "monster" (and it understands that his hatred toward it is just an extension of his hatred for himself, it hurts but it doesn't blame him). "Parasite" can be used maliciously but also sometimes fondly? In the way people insult those close to them to show affection. It doesn't understand why this is a thing but it has observed it enough and can feel Larry's intentions enough to know it, and to know when he's using it in which way (sometimes it's both). Parasite is also just sometimes used by Larry when telling random people for the shock factor. "Parasite" has more punch to it. "Alien energy being parasite thing" is also shock factor + a little more descriptive of the complexity and confusion. It also knows that symbiote/symbiont is the word Larry uses when he feels more connected to it, or is emphasizing their connection more. "Alien energy being" is more descriptive and doesn't have a positive or negative connotation to it.
The Negative Spirit will accept anything Larry calls it. Its concept of words comes from Larry. Before Larry it just had abstract concepts and ideas, not language, which is why it mostly communicates to Larry through Larry's own dreams/thoughts/memories and not through language. Its attempts to communicate with language here is just so very different to its nature. But it's had a lot of time to observe Larry doing it.
Larry is also the reason it has a humanoid form outside of him. Its natural form is just like a jumble of electricity but it shapes itself to its host. It doesn't have a concept of gender either. It observes it in others. Pronouns are never an issue for it. Including "it/its" pronouns. It understands that Larry sometimes uses those pronouns to dehumanize it and disassociate it from himself, but he also just uses it descriptively. For Larry, when it comes to pronouns for the Negative Spirit, while as I said before "it/its" can be used to dehumanize it negatively, its also just to emphasize its alien nature, and its nature as a more abstract concept because he can feel that it's more abstract than he's really able to comprehend. The other pronouns he'd use for it are they/them and he/him. He'd never think to use she/her for it, mostly because of how partner-coded it is in his mind. Although the fact that their partnership isn't completely consensual on either end (neither intended for it to happen), he doesn't associate it with his forced relationship with his wife. That relationship helped him blend into society more. The Negative Spirit makes him different, so he associates it far more with his homosexuality than with the societal pressure to conform.