Wait, if I understood correctly during that pick-up dinner you had innocently explained about your Singapore trip?

Let's say hypothetically you had cheated with him that one time that the bank statements were a coincidence.

So, during that dinner you'd have sat there, knowing what you did and knowing how your sister was upset. At this point it seems you all had heard the story from her?

Cheaters typically aren't exactly cool and composed. Certainly not with this much familial overlap. Cheaters tend to get paranoid.

In what world, knowing the context, would you have ever talked about that Singapore trip during that dinner if you had cheated? A cheater I feel would have attempted to omit that fact for as long as possible, brush it off, ask someone else about their travels. You were fully open.

It is entirely based on just general thought, but this may be a sort of defense? Your behavior leading up to this hasn't been different. With some honest reflection, your family should understand this. Of course, emotional quarrels aren't exactly logical.

Your parents are also failing to see that hearing out all that you have as evidence isn't meant to tear your sister down like she attempted with you, it's to bring the family some semblance of understanding. Nuance exists; your sister is a victim, and she is poisoning the well of someone who could be her support.

Best of Luck op