Because with his ex hyung Sooyoung didnt want his sympathy. Its Sooyoung's pride. It really because Sooyoung simply refuse his help.
With Taeseung, Taeseung just said harsh stuffs but his action were usually the opposite. Thats why Sooyoung was confuse about feeling safe. Also alot is missing the timeline i think. What we're reading now is several months after that incident at the gym. Sooyoung been working at his work place for quite sometimes already thus the progress we see now with Taeseung is like this. Taeseung had give Sooyoung time and space so he can do what he wants as long as its not something dangerous
.......uh break his other leg and arms??? wtf
like i get fierce protection and possessivenes but like......not to that extent thats kinda fucked up