Can I get honest advice ..

Okay , so ever since the beginning of time I had this dumb problem with my SO's sister . Call me childish but I really dislike her. My SO's mother & sisters live in a different state than we do. All he talks about is his little nephew & at certain times when his other sisters text him talking about his nephew I get jealous or angry , I don't know what the right word would be here . I try to avoid talking about it cause it's been a few months that I want a baby but we aren't economically stable yet .