I might be talking nonsense here, so feel free to tell me to shut up, but I think Perverteer made a mistake by not so much rushing the D/s MC/Bella angle, but by trying to take it slow like a romance.
The payment instalments should've been the hook perhaps, but say, after Dwayne gets throttled, the MC cradles her while she cries, apologises for being a jerk and lets her off the hook. Maybe after that Bella could've decided what she wanted out of it. If she decides she wants to continue, they can be honest about what's going on, admit they're both enjoying it and lay out some rules.