The thing with 'Diary of an Oxygen Thief' is that its bleak, first-person confession style leaves a mark, so you're hunting for that same unfiltered honesty about messing up and being messed up. I found 'The End of Alice' by A.M. Homes crawled under my skin in a comparable way, though it's way more disturbing—it's from the perspective of a pedophile, so the toxicity is on a whole other level of uncomfortable. For a more literary, emotionally gutting take on mutual destruction, 'The Lover' by Marguerite Duras has that same raw, almost clinical dissection of a damaging affair, but with a haunting, poetic quality.
Honestly, 'My Year of Rest and Relaxation' by Ottessa Moshfegh hits a similar nerve for me, even if the toxicity is more self-directed. The narrator's nihilism and her manipulative, detached relationships feel like a close cousin to the 'Oxygen Thief' vibe. It's less about a dramatic, shouting-match kind of bad relationship and more about the quiet, corrosive kind where you use people because you're empty. If you can handle something even more fragmented and brutal, 'The Notebook' by Ágota Kristóf isn't about romance but the toxic bond between twin brothers surviving war—it's about how cruelty can be a language of love, which is a theme that book really wallows in.