im in confusion. what does he meant by ymir choosing mikasa and how does the titans power ...

I am just as confused!!!!
How does the bit abt the Mikasa make sense?? Did i miss something??

he's the last one to inherit the founding titan because he convinced Ymir to help him earlier. so when he died it cut off all the existence of titans since they all defended from Ymir a long time ago. she chose mikasa because both Ymir and mikasa loved someone they should've have loved or loved someone that makes couldn't give them happiness. (because the king was scum and only used Ymir so she could bear his children, and even if eren liked mikasa, he died so it's basically just a very sad tragedy)

descended***

shouldn't have** sorry I cant type omg