That sounds like Gotta Sing, Gotta Dance, by John Varley, originally published in Galaxy, July 1976, and reprinted in the collection The Persistence of Vision, published in 1978. It's one of his Eight Worlds stories.
The names of the protagonist symbiont pair are Barnum & Bailey. I'm not sure of the gender (it's been a few decades since I read the story), but that can be somewhat fluid in the Eight Worlds.
The symbiote is an artificial lifeform, created from alien instructions. In the Eight Worlds stories, there's a datastream being broadcast by aliens, the Ophiuchi Hotline, containing a huge mixture of information, covering everything from science & technology, through to philosophy & religion. But you have to be out near the orbit of Pluto to receive the data beam.
The photosynthetic, amorphous symbiote has no intrinsic consciousness, but it shares the nervous system of its human partner, so they're in constant telepathic rapport, and the symbiont gradually develops its own personality.
These symbionts can stretch themselves out to maximize the solar energy they receive, which enables them to survive in space near Saturn, which has the most spectacular scenery in the Solar System. They don't require food, just a vitamin / trace element pill every 6 months or so. The protagonist, a new symbiont, has an unpleasant racist interaction with a normal human when they go to get their vitamin pill.
From the Eight Worlds article,
Usually called "Symbs", these are a semi-living material which can supply all the needs of a human body, requiring only sunlight and some trace elements. A Symb will enfold and penetrate the body of someone who wants to enter into symbiosis with it, forming a Symb Pair.
One of the side effects is that the Symb forms a personality of its own in the brain of the human. It also vastly increases the efficiency of the brain, and enhances artistic abilities.
Almost all Symb Pairs live in the rings of Saturn, trading artworks for their few material needs. Symbs appear in the novel The Ophiuchi Hotline and the short stories Gotta Sing, Gotta Dance and Equinoctial.
Equinoctial is set after Gotta Sing, Gotta Dance, and is somewhat darker.