the age gaps reminds me of this series (minus bdsm ofc) (i miss u kanda neko </3) https://www.mangago.zone/read-manga/kokoro_kanda_neko/
**spoilers warned multiple times**
-MC is naively oblivious(?) like hes not dumb about education & stuffs but dumb about love
-ML is manipulative/possessive since they were little. their family are close so they met many time and ML likes to feed MC food(MC looks like a steamed bun*we will get to this)
-there was at some point they lost and the whole nation thought they got kidnapped but ML brought MC to one of his villa and feed MC desserts(u can already sense ML is unhinged already)
-MC once engaged to ML's sis but got annulled (by ML i think) (the lil sis got married to one of ML's close knights)
-they always hold hands tgt in the palace, MC thought it was normal until the knight corrected him. ML kisses MC cheeks everytime
-the reason MC demoted many times is bcos of when they were drinking tea tgt, ML already confessed him for marriage but MC accidentally fell asleep for a sec so he didnt heard it thats why he got demoted as punishment
-every year ML send MC a birthday letter asking did MC miss him but MC replied nonchalantly, he sent a ring too but the ring didnt fit so MC send it back LMAO (the plan also working bcos the time MC was away, almost every girl are married so he doesnt have that much choices, except ML ofc)
-MC got called back to the palace as ML's plan finally see the light. 10y planning, 3yrs finding old docu, 4 finding the tablet that said same sex marriage is legal(ML is strong for this one)
-THEY KITH!! & ML asked MC to get married which MC replied yes we should, as in having rtwo weddings tgt, not get MARRIED tgt (...hes too oblivious)
-ML declared a steamed bun day(its act a facade for him to announce his marriage with MC + its MC fav food). no women allowed, only baby girls(?) & women can enter only designated area (to prevent MC from meeting girls LOL
-got disturbed by ML's cousin who got sicked in the past now claimed have fully recovered (is act obsessed with ML to the point of wanna crush our cutie steam bun MC). ML literally gave no fawks about her
may yeomin only knows warmth after this