there is no such thing as cheating being a ''mistake''The only way I'd ever forgive a cheater in a serious relationship is if it was a mistake that won't happen again and the relationship was amazing.
If its a months long affair GTFO
if it was numerous times or multiple people GTFO
if she doesn't intend to change the offending behavior (getting too drunk/high without you, partying without you, too many orbiters/attention whoring, etc.) GTFO
if the relationship was less than great or she is less than satisfied with you GTFO.
If the relationship is less about kids/marriage/partnership/cohabitation and more about short to mid term fun then you can use it as leverage to transition into an open relationship or downgrade to FWBs/plate status or something.
Never try to read a woman's mind. It is a scary place. Ignore her confusing signals and mixed messages. Assume she is interested in you and act accordingly.
Quote taken from The SoSuave Guide to Women and Dating, which you can read for FREE.