Word to describe a relationship that fluctuates between being good and bad

I’m looking for a word to describe the dynamics of a relationship that oscillates between being loving/harmonious and toxic.

By relationship, I’m primarily referring to a romantic relationship between a couple, however it can also apply to any (romantic, familial or platonic )relationship.

I hope my question makes sense. Grammar savants feel free to edit my post.

up-and-down (or up and down) relationship

mercurial relationship

https://books.google.com/ngrams/graph?content=up+and+down+relationship%2Cmercurial+relationship&year_start=1945&year_end=2019&corpus=26&smoothing=3

While I'm not sure if this qualifies as a "single word", I can't believe nobody has suggested love-hate relationship yet, which has all sorts of rich metaphorical usages beyond sexual relationships.

Wiki also links to on-again, off-again relationship, which is typically but not exclusively used in a romantic context.

And for Japanophiles, tsundere describes a similar dynamic/perennial trope of teen romance stories, which has been enjoying a steady rise in usage since the turn of the millennium.

Such a relationship can be termed bittersweet.

M-W:

bittersweet adjective
Definition of bittersweet (Entry 2 of 2)

1: being at once bitter and sweet
especially : pleasant but including or marked by elements of suffering or regret
a bittersweet ballad
bittersweet memories