Is my sister jealous or whats her problem?

Im getting married before my oldest sister. Ever since i told my family i was getting married he startedbto be really mean to me. She always has something negative to say about everything i do. Talking in the phone to my bf bother her. She has a bf too shes been with him for 7 years. He is pretty lazy 30 years old and jobless. He uses school as an excuse. She is embaressed sometimes to go out with him. My bf is hardworking and treata me good. She is always saying mean thins about him. He never says anything about her. The worst thing is that my mom takes her side!! What is there problem??