I can deeply appreciate your pain and the struggle in your current situation. I want to challenge several things about the choice to return to your girlfriend and what is happening with her sister. I want to highlight the use of your pronoun when discussing how you were going to heal with your girlfriend. You said: “…I decided to make it work…” This is very telling because you didn’t say “we”. Nowhere in your discussion of these events do you speak about what your girlfriend has said done or promised to do to make things better. If you thought it was only your decision that would make the relationship better, the effort was not destined to succeed.
From what you’ve explained your girlfriend betrayed you, kept secrets, and then falsely accused you in a few different ways. Her sister also seems to be lying and making up stories as well. My question is: are either of these relationships worth your time and effort? Why would you want to make something work that seems so deeply flawed, convoluted, judgmental, accusatory, and inaccurate?
Whatever your girlfriend’s reason was for cheating what she didn’t do was be honest with you. Whatever her sister said or did was either a lie or misinterpreted. Either way, you are not going to be in a position to change this situation, and, quite frankly, it is hard to imagine why you would want to. What is happening with your former girlfriend and her sister seems to have little to do with what you know to be true. It is time to unhook from this family, learn what you can from this situation, and find a relationship with someone who will treat you better. You deserve it.
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral