I could use some serious feedback?

In my culture dating is not accepted. I have a secret boyfriend, and I wanted to tell my sister (she’s okay with me dating.) I was ready to tell her about him, and I really wanted my boyfriend to meet her, as it’s the only family that he can meet as telling my parents is not an option. She told me today that she will never cover for me when I want to see him (ex. say I’m with her when I’m really with him). I’m heart broken because I thought I could trust her, and that she’d help me develop a real relationship with him. What should I do, should I tell her about him, do I have a right to feel this upset?