So sorry you're in this position mama, and so sorry that you have had permanent issues from your tear.
I had a 4th degree tear (from forceps) during my first birth. Healing was very painful and difficult. However, a full year after the birth, I was about 95% back to normal. By 18 months postpartum, I was 100% back to normal. I can honestly say that, other than an actual visible scar, everything about that area is back to normal. I had my 2nd baby at home in the water, and had just a very superficial abrasion with him. I realize how fortunate I am and I wish the same were true for everyone.
My point is, though, that even a 3rd or 4th degree tear is not a guarantee of permanent injury or lifelong issues. Moms like myself have had severe tears and have been able to heal and recover normally without problem. Maybe you had a poor repair job done, or maybe just bad luck, I don't know. But I wanted you to know that even if you were to choose another vag birth, and if you were to tear badly again, it's not a guarantee that your recovery would be as bad as it was the first time.
Thinking back to my bad tear, and thinking about that vs. a c-section, I would choose the 4th degree tear a hundred times over. But I had a good outcome and you did not. And there's no way to predict which way it's going to go. I hope you are able to make a decision you are comfortable with. Good luck to you!