I would not admonish you for the feelings you are having. But things get sticky when one tries to act on such feelings.
This is definitely a topic that is extremely touchy in the real world.
It is often conflated with molestation, rape, and anything that is Not consensual. (I'm writing my response with the assumption that your cousin is not a minor.)
Most people would not even allow themselves to think about it in the terms of two consenting adults.
And if they get that far, they can only think of it as an abominable sin, a criminal act, or in terms of their own familial relationships : Aka "eww I could never think of so&so that way."
A lot of these reactions are not thoughtful and are not bred from any deep discussion on the subject. Because no one wants to talk about it.
That said, I would never enter the minefield that is incest even if I was ever to find myself in a similar position as you.
I do think the possible birth defects and likely societal humiliation (if it got out) should deter anyone who entered such a relationship from having children. Whether or not the science on that is disputable, you would still risk bringing children into the world that would have to deal with the backlash.
The main issue I personally think is
most dangerous/destructive-is that unless you are the last two people left in your family, any pursuit of this could disrupt the entire family structure.
It could rock the boat until the whole vessel and everyone on it sinks.
In most extended family dynamics, the familial relationships are on the same level so to speak, all sharing the similar 'familial love'.
When you single out another family member into a romantic or sexual relationship, you can not only end up hurting yourselves but the rest of the family as well.
There can be a lot of complicated feelings on the whole affair from every corner.
It can even invoke a strange sort of jealousy or a rejected type of response.
No one else in the family may want to be romantic or sexual with you, but they may have feelings or thoughts such as "Why is that person more special than I am? Why did they choose them? Why aren't we as close?"
Think about it almost like favoritism among parents and children..how destructive that ends up being. What it does to the psyche of the children second in demand.
Especially if it is obvious.
...And then there can be feelings of guilt or failed responsibility from the adults, anger from protective siblings or parents, questions of whether one coerced the other. It can go on and on and it's a big mess that can never be swept under the rug once it's given life.
You also risk your own relationship with your cousin if you tell her. You have to decide what is more important to you. The cousin relationship, the bond of blood,
which I think on its own, is very special.
Or the possibility of a different kind of relationship. Which is not as absolute as the former. And by your own words, unlikely since you believe she would not feel the same.
If that ended up being true, it could ruin ANY type of relationship you have with her.
This is not a simple 'follow your heart and don't look back' type of situation. Regrets are to be expected.
Then there's the whole reason you are here. What will this do to your mental health if it doesn't go the way you want it to? What will it do to your heart?
You've got to protect yourself as much as anyone else in this scenario.
I don't know your main reason to CTB or if this is something you believe would positively affect your state of mind if she reciprocated your attraction. Or even if it's something you just want to get off of your chest and you will ctb either way.
I have no idea how far you want to take these feelings. Just that I don't think you deserve to beat yourself up about it.
So all I can ultimately say is weigh the risks vs the benefit. Give it careful thought and attention. Basically sleep on it..heavily. You even gave some credence to the suggestion that the feelings may have manifested as a result of not being around any other people. And that's a perfectly possible explanation.
Either way, sorry you are struggling with this.
