Cookie for you dear! You won bingo lol
I found chap 4 and 8 here
https://mangafire.to/manga/starting-today-i-will-forget-you-so-i-wish-you-happiness.zkl72
I can summarize it if you're really curious!
Spoilers ahead
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Chapter 4 has her waking up with amnesia. Somehow she's so calm about it lol. Ig her subconscious is deeply over it and happy to forget. She mostly just reconnects with her childhood friend but when she finally decides to return to school after over a month of rest, CP ambushes her and even when she goes, "Who are you?" and "oh, you're my fiance?" from picking it up when ML and CP argue, CP momentarily deludes himself thinking she remembers him... gross
Chap 8, no worries dad is just testing him and true enough, ML was thinking too shallowly. Going home, he did meet some resistance from his family bc switching factions is a big deal but eventually convinces them and proposes to FL. She agrees and love him too.
Meanwhile, CP is no longer CP ha. His parents make his 12 yr old brother the new CP and admonish him for being too egotistical. His school days are all closely monitored as a final examination and he did absolutely nothing. He secretly agrees to his demotion thinking he still has a chance bc his brother is still young but jokes on him he gets informed that his side piece is in jail bc she's pregnant. He had no clue bc he denied all her visits. She ofc claims it's his but who knows really... truly his final nail in the coffin lol
School bike? She's the public street honey. Atp we don't know for sure and idk if they have a way to identify bloodline but if it really is his, his surprisingly responsible parents would probably have him demoted further and maybe even marry into her poor family estate instead. No way they'd ever accept the [innocent but time bomb] child. He can kiss that reinstated CP dream goodbye... part of me kinda wants that. Trash belongs with other trash after all

Ok...let's get some things out of the way...
First, the fourth chapter is from another manga. Please fix it.
Second, how many guys did Maria screwed and how did she not get STDs or pregnant?
Third, Didn't the Duke learn ANYTHING from seeing how his daughter suffered as the Idiot Prince's fiancee?