This reeks of “go directly to couples therapy, do not pass GO, do not collect $200,” which sucks because that $200 would be useful for paying for the therapy.

Get rid of her. If she hasn't cheated already she is about to. I mean cheated physically. She has already cheated emotionally. She has YOU to talk about sex. Not her ex. Find someone who needs only your reassurance.

Maybe. You should keep "throwing it" in her face, but maybe mix things up and sometimes "throw it" on her ******* or up her butt or on her belly. Don't be boring!

This one depends a lot on context. If girlfriend was feeling inadequate because of yours and her sexual life; especially if you had made her feel inadequate - Then she might have been trying to figure out if the problem was her, you, or the relationship. It would have been much better for her to speak directly with you about whatever the issue was, it’s not necessarily the beginning of the end for the relationship… If you want to just end the relationship just keep doing what you are doing. If you want to save the relationship, try to discuss your issues calmly and figure out if you or she or both of you need to make some changes. Address the issues about you and her - not about the ex.

If your girlfriend was asking her ex, this means that she isn't enough for you sexually?

You're only wrong if you continue to stay with this two-timer.