I'm so sorry.
I wasn't flat out told that it was my fault or that I should allow him to cheat. But, I was told by many family members on both sides that sometimes "these things" happen in a marriage and we should stay together for the kids sake. My own mom told me the day after DDay#1 that there would be no divorce because marriage is forever.
Both of my parents are madhatters. So, of course if they had to stick it out then so did I.
DDay#2, several years later, I was done. I wasn't going to put up with the cheating again and it didn't matter what anyone had to say about it. My mom was holding out hope for weeks after I left that STBXWH would come to his senses and we would work it out.
No one should ever be in a relationship where they are expected to let the other person lie and cheat. It's abuse and I'm so sorry that your mom doesn't see it that way. And, I know that lots of people have said and you know it deep down but it deserves repeating... You are NOT to blame. Me: BW
DDay #1 Tried R
DDAY #2 Divorcing
Burn everything love then burn the ashes.