Think about what might constitute the structure of your relationship.
Do you see a platform; a stable base of love and support from which both people can reach for their dreams and ambitions?
Or do you see a prison? A restrictive environment in which your every move is monitored, judged and criticised in return for some vague notion of 'protection' or 'security'?
If you're seeing the prison, it might mean that your relationship isn't doing much for you. In fact, it could be actively stopping you doing the things you want to do in your life. Whether that's going out with your sister, or thinking, 'to hell with it! I'm going to apply for that dream job in Australia!'
From your posts, you come across like a kind, articulate person. (You write well and with clarity, by the way. Nothing wrong with how you've worded anything.) You deserve to decide how you live your own life. And you have a lot to give - to the person who is worthy of that gift.
Don't fall into the trap of thinking that there are only two settings - be in this relationship and never go out, or leave and have a wild time. There's so much middle ground. If you're not a wild person, you don't have to be - but that doesn't mean you have to stay in a partnership that isn't supporting you. Likewise, if you do stay in the relationship, it's not unreasonable to expect some control over your own life - including deciding that you want to go and have a laugh over some drinks with your sister, or, I don't know, meet new people by joining a mountaineering club or something.
I would imagine that it's very difficult to see any context, as you've been together since you were 15. So you don't have any adult experience of life outside this particular relationship. You have to imagine it, and that gives your brain licence to make up all sorts of terrible things that might happen. Also, you have limited context to be able to see when something isn't healthy. But your subconscious knows; otherwise, why would you have posted in the first place if you really thought everything was all beer and skittles?
I think posting on here is a good step, you should keep doing it. There's a community of people here who have been through situations similar to yours - and many much worse - who will lift you up and support you if that's what you need. (Although telling you what you want to hear isn't part of the deal!
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