Nothing out of line here. I really don't suspect anything, and my paranoia has led me to ponder that possibility more than I probably should. She was cheated on in a previous relationship, so she's fiercely against it. I'm confident she'd split up with me before she cheated...or immediately after.
Haha, that's a typical move. Her mistake though, not your fault she now has to deal with the consequences of her own actions.
