Parents keep letting my sister go out but me. what can I do?

My parents always treated me and my sister equally. However, when it comes to going outside with friends and what not, they would take gladly take her and pay for her friends as well where as me, the older sister with a boyfriend, can only expect a harsh no as an answer in first attempt. Their only excuse would be "she's only going out with friends and you're going with your boyfriend...". I'm a teenager (turning 16 soon) and I think of myself as a pretty decent kid who hasn't really done anything wrong or has gone beyond parents wish behind their back, plus on track with my academics and never took or did anything like alcohol or partying. I've had my boyfriend for more than an year as well and it's healthy mature relationship where both of us have kept our limits and not done anything too bad. My parents have also been aware of whenever I would go out with him, where I was and what I did. While knowing all of this, they still won't let me out and my 13 year old sister can go everywhere. What can I do about this and how do I make them understand this?

Parents keep letting my sister go out but me. what can I do?
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