The Lady's Tutor by Robin Schone

Welcome to Robin Schone's The Lady's Tutor.  She's a wealthy Victorian politician's wife, proper in every way.  He's a halfbreed bastard... oh god I can't with this racist book, I just can't.  It's about a woman who asks for sex lessons with no lab component, and then she realizes her husband sucks and opts for the lab after all.   This is one Sara had very fond memories of that... did not necessarily hold up.  It has some major content warnings - it's got Evil Gays complete with political pederasty ring.  It's a sheik book - the kind where don't worry he's mostly white anyway.  It's got literal gaslighting (they threaten to have her institutionalized and when the threats don't work they try to murder her by blowing the gas lamp out.)  It's the first book we've read that's obsessed with penis size.  It's got some genuinely strange sex scenes in it.  (Pro tip to any aspiring romance writers - the word "cervix" is never sexy.)  It's got some seriously nasty body shaming directed at the heroine from her awful husband.  It's got attempted murder by Spanish fly.  It's a whole ass mess.