Look , I know that princess is not fit to be a queen but it doesn't change the fact they are engaged ( think author will make her do something bad so we'll hate her later)
So here the prince is a cheater and MC is the 'other girl' doesn't matter for what reason, it is what it is .
Like if it had a "i possessed/Reincarnated as a villainess" trope , prince would be described as an ass who cheated on his finace and i can't unsee this
And i dont understand that why that count was a peice of shit in last timeline and now he's all good