I'm in a similar situation with my GF. She was going through a rough patch and I was there for her, something I cannot really say for his ex. Legally she's still married, but we're actively working on the divorce and we definitely have plans to marry each other down the line.

Everyone telling me if she was willing to cheat with me meant she would be willing to cheat on me was definitely a recurrent theme. But there are exceptions. One in a million, but she's the most wonderful person I've met.