@HarleyQuinzel
It seems the original Dylan was the villainess. She tried to seduce her brother-in-law on her sister's funeral and even got married to someone else to be able to persue him more. Thankfully, she got replaced/isekaied by this delightful mother-bear Dylan.
And the FL was not a thot. She meet the ML after his wife's (and son's) death while he was drowning his grief in booze and gambling.
@KenOne sheโs literally doing what you just said, preventing her sisterโs death because nobody else can. She clearly said she doesnโt have a grudge and really wishes him happiness just with someone other than her sister. How the hell is she irrational?