Perhaps she just felt a little left out that others around her had relationships so she thought that she would make one up to make her feel like she's part of the group. It's not entirely uncommon, I've seen it happen before.
Or, maybe she's just... promiscuous. Maybe she left her boyfriend because she knew that your ex was a "better catch", so to speak.
Whichever it is, I wouldn't recommend confronting her. After all, like you said yourself, you don't own him, and plus, you broke up with him. Ask yourself if it's really that important, because it's best not to waste your time on trivial things like this, trust me, he's not worth it. Especially if YOU broke up with him. Although, I guess if he broke up with you that's more of a reason to hate him and not care. [ dotdashandy's advice column | Ask dotdashandy A Question ]
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