His ex reached out. What should I do?

When we met he was single. He pursued me for several months and during that time got in a relationship with another girl. He dumped her when we got serious. I had no idea about her until a couple of months into our relationship. I felt awful because I’m not the type of girl to mess with someone else’s man.

I guess she found me on Facebook. She sent me a message the other day asking if we could speak so she could gain some clarity on things. What should I do? Just ignore her? I feel bad and I feel like she might want closure but I think talking to me will only make her upset. She doesn’t know for sure that he cheated on her and broke up with her because of me. She thinks he broke up with her because he was never all in with their relationship and met me right after.