They were still "together", but she was living in Hawaii when she cheated on him. (Doesn't make it right, but we've got to keep to the facts in the letter ....)
The bottom line is that she couldn’t be trusted. After he broke up with her, and had her name taken off the credit card they had shared, she charged $600 of stuff to it, then lied when confronted. She only admitted to it when he threatened to fine charges of fraud against her. She’s a liar, a cheat, and a thief, all rolled up in a little ball in her hippocampus.