First off, thank you for your vulnerability here. I know that's not easy. I'm glad my piece could offer something you resonated with enough to share your story.
What you've got going on with your connection sounds incredibly challenging, exhausting, and painful. I think it's a great sign that you can clearly recognize and put a name and description to the patterns of toxicity you're seeing in your dynamic. Awareness is always the first step in the process of healing. Awesome job on that!
The second is acceptance of where you are, acknowledgment of what you need to do to heal, and then, of course, taking action to do so -- be that through communication, grief, forgiveness, surrender, letting go, etc.
I know, personally, how difficult it is to separate oneself from these connections. Energetically, it's pretty much impossible. If you are twins, you're one in the same on that level. Fighting that reality brings more pain than it does freedom. Detachment, however, is possible (I've written about it in another piece, actually, in detail). But it's always work, and you have to surrender to what IS in order to do it. Acknowledge what you feel from her, the ways she still speaks to you, the ways you still love her, and you hate her for not being able or willing to show up in the ways you want her to.
If it helps, talk to her in your head. Tell her how she's hurt you, how frustrated all of this makes you. Instead of participating in the toxicity on the 3D level, and then trying to block her energetically, leave the 3D interactions alone and engage with her energetically. Be open and honest about the hurt.
Let yourself grieve it all, and honor how much it sucks.
And then get to work on pouring into yourself, instead of staying wrapped up in the stagnation and cycles that this connection has perpetuated for you. I see you're working on healing some insecure attachment -- that's a beautiful and wonderful place to start that self-love journey.
As you fill your world with things that bring you comfort, peace, and joy you will attract people who align with that energy and want to contribute to that in your life. Your twin MAY be one of them one day. Or she may not be, but either way, you'll find the energetics of the connection will start to shift and ease when you're disengaged from the drama.