Why, though, do we so often feel guilt when we make what we know intellectually is a survival decision? This guilt predisposes us to returning to the abusive situation or seeking out new abusive situations we can 'do right this time,'and in the meantime poisons the air around our new freedom. Are we faulty for experiencing these feelings? If we feel them, are they legitimate indications we're in the wrong? No, and I'm prepared to explain what's unique to separation regret in abusive situations.
1: Surviving hardship builds powerful bonds even when the bond partner is the source of that hardship.
When we go through hard times alongside another person, we tend to get attached. It's part base survival instinct - "You're in this, I'm in this, we're getting through this, you're probably a friend," - and part human empathy. You grow close through shared experience, and if you both make it out your animal brain associates that other person with security.
This is all generally helpful, except we're not all that... well-programmed, to identify instances in which our comrades in arms are actually generating most of the problems. In the moment, we tend to think things like "We have so little money for things like medical care," without appending things like, "because my parents spend the majority of the household money on their habits." You might remember that time in your life when you were really struggling to complete your degree, but you're less inclined to remember that your live-in boyfriend contributed nothing to upkeep of the household and kept you up all night performing emotional labor for him.
These guilty parties are contributing to the group struggles - your parents aren't doing better by being both addicted and without dental care, and you boyfriend isn't benefiting in the long run by sabotaging your combined potential. We wouldn't screw ourselves over that way, so it's hard to imagine somebody in our shared situation is the architect of that situation. But they are, fairly often, and rely on the combined powers of trauma bonding and assumed innocence to keep their supply - you - close at hand.
2. Even if they don't always succeed, abusers work very hard to make the prospect of leaving materially and emotionally daunting.
Abusers preach the virtues of 'loyalty' and the insolubility of certain bonds for a reason: There aren't a lot of other reasons to spend time with them or help them. Their survival - emotional and often material - depends on ensnaring people in constructed situations in which the abuser is sole distributor of material and emotional security.
Your guru takes your paychecks and the proceeds from selling your house. Your parents raise you in seclusion without a proper education. Your boyfriend intercepts your letters home, guts them, and types up new letters to stuff in the envelopes you've addressed in your handwriting. You have no money to live on alone. You have no friends or teachers to turn to, you don't know what normal is. Your family receives 'your' letters in which 'you' disown them.
You have nothing or next-to-nothing, you are isolated, and a single person remains who will - between bouts of cruelty for which they take no responsibility - show you something like kindness. They control all the money, they decide when and what you eat, they are your only real human connection. Everything else feels so bad, and they're a source of the good feelings.
But this is all by their design. They disguise the modest breaks in their deprivation as kindness and trust you'll feel guilt along with the fear you'll fail at a life without them.
3. Admitting culpability or vulnerability in a chaotic, tyrannical situation is in itself traumatizing.
This also belongs on any list detailing why people stay in relationships with dangerous people. Why haven't you left the husband who batters you and your kids? Why are you still in the cult and cheering for all the weird, evil shit they do to other people? Why haven't you left the girlfriend who steals your things to fund her Fentanyl habit?
Because facing the possibility you've built a significant portion of your life and identity, spent money and time and resources on, defended and aided and abetted for months or years terrible acts, on the foundation of a huge mistake is terrible. It hurts to admit you fucked up, it hurts to admit you're manipulable and vulnerable and fallible, and every time you refuse to cop to your mistake you proceed deeper into the lie and deeper into the storm of destruction to your life and the lives of others and the hurt compounds.
It sucks on toast to acknowledge, "Yeah, she wouldn't have killed my cat if I left the day she pulled the china cabinet down in a rage. She wouldn't have even done that if I refused to let her move in with me when she'd already brazenly signed up for credit cards under my name."
It hurts to be that person everyone wants to ask, "Why didn't you tell anyone? Why did you let him talk to you like that?"
My own therapist asks me, sometimes, why I kept the goings on in my house secret until I was an independent adult. I think ultimately all these factors lap together into one overarching answer: Abusers design your world and your experience of yourself all in the interest of keeping you silent and dependent. You feel bad when you leave or disclose because you've been engineered to feel bad about it.