There are other ways to damage besides straightening. Did you use permanent dye? That can raise porosity as well as lead to dryness. How often do you blow dry? That can also damage. You mentioned you use CO. It turns my hair into a dry brittle horrible tangled mess. Also I have had to do some cuts a few times after protein overload. It took weeks of intensive dc's to recover.

If your hair really is to the point of no return Your choice is you can either cut or learn to live it until it grows out. You might ask yourself what is more important to you health or length. I will say if you have a bunch of split ends i suggest you hurry up and cut because it will get worse.
"A life without fame can be a good life, but fame without a life is no life at all." - Clive Davis