^^^
The rat didn't die because the took the light away, Venice. It didn't die because it lost hope. Light signifies hope it that experiment, right? It probably served as Hope too for the rat. But when they took the light away, it actually got disoriented. The rat isn't physically equipped to keep swimming, so being in that position without any direction, no light, nothing to see, instinct took over and it probably panicked to the point of drowning. That doesn't happen to a real live person because his reason equips him to logically assess the odds and compliment it with a counter reaction.
Let's take on another experiment. Something that involves an animal with more brain power and more human-like instinct. Monkeys.
In this experiment they placed 5 monkeys in a cage, that had a banana attached on top of a pole. When a monkey tries to get the banana it triggers a cold shower that sprays all the monkeys. After a few runs at the banana the monkeys stops the attempt. What they do now is replace 2 of the monkeys with brand new ones. The two new ones of course, immediately goes to grab the banana. The other 3 (original monkeys) stop the attempt to the point of beating up the 2 new monkeys.
They turn off the cold shower, replace the 3 original monkeys one by one, with 3 new ones, and what happens? Everytime a new monkey joins them and makes a run at the banana, the other monkeys gang up on him and beat him. Why? Not because of the cold shower anymore because these new monkeys haven't experienced that yet. They just beat the monkey that goes for the banana simply because .... that's just the way it is done around here. And that, my friend, is how Company Policy works.

Ha-ha-ha-ha.
But seriously now, my point is, if you look carefully at the traits that makes an abuse victim you'd notice that a lot of them are accomplished, promising, intelligent, and competitive women. Easily, the best at what they do. Which in turn makes them PROUD women, ... or at least that's how the world sees them. And such Pride is what got them to stick to the abuse.
They think of the ideal, and unconsciously associate themselves with that. Unconsciously, as go-getters, they associate themselves with "perfection" too. Or at least are so passionate about it, that just like the new set of Monkeys, refuses to give-up the relationship because apparently, that's how to live one's life perfectly, .... or at least that's
what everyone does.
That's what everyone expect you to do. Successful people have successful relationships. That's how everyone sees it.
There's a chance that your fear doesn't center on saying goodbye or being alone. It could be that your number one fear is Fear of Failure. That even to the point of being abused, you refuse to give up and would rather slug it out hoping that a spotless record is still attainable.
So how do you start letting go?
First, You have let go of your marriage. Not that it's not workable anymore ha. But because you can't fix it while you are nothing more than the relationship's victim.
Secondly, let go of your Pride. You can prove that once you have enough courage to share your ordeal with people closest to you. Believe it or not, the way out of this slump is total acceptance, humility, acceptance of failure, coupled with the will to give what you deserve justice, then eventually the desire to move past the abuse. ... Or that's what I heard. If it were me, I'd simply say "Call the cops on him".

If you're going to give-up on something, Venice. I suggest you give up on him. You give up on your Relationship. But never, ever, give up on yourself.
Here's hoping that helps.