Every dark romance list on the internet either apologises for itself in the first paragraph or dares you to keep reading. Neither is useful. What you actually want is a shelf where someone has already done the work of saying how dark, in what flavour, and whether the payoff lands.
So that's what this is. Nine books, each with a heat level from 1 to 5, the spice types that actually apply, and the content notes up front — not as a warning label, as information. You get to decide what you're in the mood for.
A note on ordering: this list is not ranked by intensity. A 5-flame book is not further along some path than a 2-flame one; it's a different flavour. The slow burn at number three took me longer to recover from than the unhinged one at number seven, and both of those are true at the same time.
If you finish any of these, log them. Tag the heat, tag the spice types, tag the tropes, tag the warnings — all as separate layers, none of them ranked against each other. That's the entire premise of Forbidden Folio, and it's free.
If you want the definitions behind the labels, The Scarlet Pages has a longer piece on what dark romance actually means.