On page 24 he talks about Ines’s ‘needlessly good memory’. It’s a clear hint he knows Ines has memories and it automatically implies he also has memories. The context of his statement also makes it clear he is talking about memories of past lives.
https://www.mangago.zone/read-manga/the_broken_ring_this_marriage_will_fail_anyway/uu/br_chapter-248232/pg-24
And no, you’re not dumb. The original story is written more like historical literature and that means it’s not always easy to understand. The manhwa takes lines directly from the original story so it’s similarly challenging to understand in some places.
Oh got it, it makes sense now thx ╮(￣▽￣)╭
How did everyone get that Oscar still has memory from the past life? Did I miss a part?