You have a lot going on in several areas. I have questions about them. Could you be willing to clarify where you stand in each of these areas?

(You don't have to if you don't want to.)
ONE
Her need is primarily reassuring her that this won't wreck our marriage.
So... what behavior does she plan on doing to help sustain the marriage?

So far she doesn't communicate with you, and she doesn't date you so you too feel appreciated and special. If all her time is going into dating new people then where is the time spent dating you?
Does her definition of "Reassure me that this won't wreck out marriage" mean "I want to poly however I want while I take you for granted and neglect you. And I want you to not complain to me about it." Is that what she thinks "successful marriage while poly dating" is? That's what has to happen so the marriage is not "wrecked" to her?
If that is the case? Then no wonder you feel unstable and insecure in this relationship. The problem isn't you feeling unstable and insecure. Your feelings are right for the situation. It just ISN'T a stable or secure situation for you to be in where you could expect to thrive.
The problem is getting you OUT of the shaky situation, not you changing your feelings or ignoring them/becoming numb to them.
TWO
I wonder what you get out of poly. What ARE you getting out of this new Opening?
I wonder if you agreed to Open again hoping that she would appreciate the gesture. And to show her appreciation, she would get around to dating you too instead of taking you for granted.
Is that it?
THREE
You could be more specific about behaviors that could meet your needs to see if she steps it up. You seem to have a hard time articulating.
If that is the case, I could see why she doesn't want to get into long conversations about your feelings. It's your job to know and state what you feel and what you need to solve it. If you sit around going "I feel bad. I want to feel special" and she's asks all these questions to try to help you identify what thought or behavior led to inspiring this feeling? And what specific behavior you want that leads to you feeling special? It's like fishing in the dark forever or trying to be a mind reader to speed this process up.
If that is happening I could see why she might go "Ugh, not again! I don't want to be sitting around killing several hours helping you fish! Figure it out, then make a request when you actually know what you want to ask me for."
There is a world of difference between "I feel bad. Could you reassure me?" where the other person has to be guessing what behavior you want.
And "I feel annoyed when you park the car in the driveway and block me in. I cannot get out like that because I don't drive stick and cannot move you car myself. Could you be willing to park beside me rather than behind me? When you consider how your behavior might affect me, that helps me feel important and special to you."
The first is vague. The other person could say "I'm sorry you feel bad" and you might even feel better for a bit. But it circles back around because nothing specific was solved.
The second is specific behavior. Something can be changed. And hopefully you stop feeling annoyed by cars blocking you. It gets solved because it does not circle back around.
Could taking a
need inventory help you list what it is you need? You could print and circle which ones apply.
Do you need to take the
feelings inventory?
But if she's still not meeting your needs even after you list specific behaviors? You get nothing enjoyable out of it?
You could withdraw your consent to poly.
FOUR
It did not go great that last time you two tried to have an Opening. Something has to change for this Opening to go a bit better.
I agree with the others about a "checking in" time. Not spend hours doing it, but 15 min for you and 15 min for her sounds like a doable check in once a week, and then dial it down to once a month or less as you get past this initial transitional time. It is
normal for things to feel weird. The "old normal" is gone, and the "new normal" isn't fully here yet.
But before you even go doing things like "check ins" -- be sure you even
want to be Opening and doing poly.
Polyamory has a way of magnifying all the cracks that were already there. If you were being taken for granted in the marriage before poly? Could have stopped to repair that first and then Open from stronger foundations.
FIVE
Are you both willing and able to see a poly friendly counselor to help you navigate this transition time? Assess what areas need strengthening? I don't see where you answered that.
What other things might you be willing to do to help this Opening go better than the last? When do you stop trying to Open? What are you NOT willing to do?
I am concerned that maybe you floated along into this, and that's part of where the discombobulated/insecure feelings come from. That maybe you don't have firm boundaries about what you will and will not put up with and feel helpless or rudderless or something similar. When really you are the captain of your own ship and you decide what you are and are not up for.
Galagirl