@TheLetterTen I hope it's ok that I slide into the replies •snap• again. It sucks big time! But it also seems like your thought pattern is something called "catastrophic thinking".
Here is a reasonable PDF on the subject: https://www.mhinnovation.net/sites/default/files/downloads/organisation/catastrophic_thinking_and_how_to_stop.pdf
Cheating is never, EVER the fault of the person being cheated on. Cheating is always the fault of the person too selfish or cowardly to do the decent thing and talk.
I have never been cheated on that I know of (yay being aro ace I guess) but several people I love dearly have been and it always makes me absolutely livid! Especially because those people are absolute sweethearts who are as loyal and loving as they come.
It's not your fault. It's truly not, and fuck both of those women for making you feel like it was.