Exactly! I was like how did this happen so suddenly…
That's the Leonia effect... not only she mellowed him down over the years... and probs nagged him about romance since she knew what was to come... but she likes Varia... a lot... and her opinion also reflects on him. It's the same with Varia in regards to him... without Leo's pushing it would take a lot of pining and pushing and pulling and trying hard to deny feelings and misunderstandings and time and all those little things that annoy readers in the northern duke cliché... things Leo is well aware of and trying hard to nip!
But mainly yeah... Leo's unfroze his love/feelings circuits before Varia came... the FL slowly defrosting them is usually what takes time... hence why... â•®(￣▽￣)â•
It only feels sudden because he didn't suffer a strong case of Northern Grand Duke Syndrome
Hot take but its hella sudden like wdym stone cold untrusting duke of the north fell in love for what was probably less than a year? Not even a little pining?????