Moo Yeol and Yoo Jung are star-crossed lovers ---- According to description, FL's sister need to die to fulfill this star crossed lovers

we saw in very first episode ML kill his girlfriend, it was shown as accident but it was a murder well planed as accident
then this man find girlfriends sister after 10 year WHY because if he found her 10 year ago she would be minor and our ML can not be shown as Pedophile so 10 year time gap for convince

why ML should be forgiven for murder because he is ML and handsome
why FL should love her sisters boyfriend because ever sister like to steal from there sister even after there death