Then you absolutely need to revisit this conversation with your girlfriend if you ever hope to move forward. Otherwise, you need to break up and start focusing on your own life and what makes you happy, so you can move on and find love with someone else in the future.
to be honest, her body is her business. that miscarriage wasn't anything to do with you so its none of your business. Who was the guy exactly? if it was the guy that knocked her up, then ask her why she felt more comfortable going with her ex than with you.