Jealousy Support Group
Jealousy typically refers to the thoughts, feelings, and behaviors that occur when a person believes a valued relationship is being threatened by a rival. This rival may or may not know that he or she is perceived as a threat. If you or a loved one may have an issue with jealousy, this community is a good place to start exploring the issue and get support. We're here for...
And if she says they're your ex's why should it matter. Say because you and that guy obviously had a connection and to have her sleep with him is painful..
You're not jealous, you're acting like a human being.
You need to show your sister that she should think about your feelings before possibly breaking your heart.