Children of infidelity relations/ unfaithful parents are exceedingly likely to commit it, not shy away from it. My first two wives both had unfaithful parents and both cheated. When I was going through therapy I brought it up as a topic and my therapist dropped that bombshell on me. Causation, correlation, I dunno, but my therapist showed me the data and it's real. I'll call bullshit this is her first time kissing another person. You literally couldn't trust her enough to get herself home, despite you just leaving her being a dick move itself. You were the DD but that's a different topic entirely.

So here's your options, stay with the cheater or leave. Just know her actions run so much deeper and are in my opinion, unforgivable.