a novel about a commoner girl who enter an academy and got propose by a marquis heir...something about the child born by her will have powerful magic...her friend is actually a spy who later found out that the girl was actually a descendant of a duke household. her father is the third son who choose to live as a commoner... thanks in advance
https://www.novelupdates.com/series/the-magic-academys-romantic-circumstances/ I think this is the novel you wanted.....but the link is dead. Not sure if wayback machine will be useful. I remembered reading it once and it fit your description.
yeah this is it...but omgg why is the link dead T-T...no wonder i couldn't find it thanks you anyways