Hello redditors. My (20M) ex broke up with me back in February and got engaged to a guy she was dating for two weeks in April. Now she’s checking on me. What should I do here?

So yeah. Title explains it a bit. Little extra important info. Me and my ex fell in love very quickly. It was a feeling I had never felt before and have yet to feel again. I would’ve done anything for her and she knew that. Anyway, she broke up with me in February (I started the conversation though) and my world stopped for at least a month. It was pretty sudden. It was among the worst emotional pain I’d ever felt. It was neither of our faults though, for the record. She still loved me but couldn’t do it anymore because of her situation. Anyway, So what happened is about a week ago I was hanging out with a girl, who I was interested in (and eventually ghosted me ) and posted it in my insta story. My ex, three days later texted me for the first time since early March and asked if she was my new girlfriend. It was out of the blue and confused me a little bit, as she is engaged to a guy she dated for just a couple weeks. I’m very confused. It’s been on my mind since then. Should I ask her why? What should I do? I know it’s a shit show but bare with me here.