Sorry but, he's saying that to be a better person for her because right now he isn't in the best state of mind, and he realized that too so he's improving. That's what she wants, for him to be okay. So, it's not one-sided at all, the both of them are just doing what they think is best for their relationship to develop further unlike before where Siyun was overly obsessive to the point where it got toxic.
And he's just kind of mentally ill, not really much of a flaw.
I just wanted to inform you btw, not to be rude or anything it just rubbed me off the wrong way and thought that you may have gotten the wrong idea of that line (⌒▽⌒'')
Haha that's okay. No harm feelings just a mere thoughts. (=・ω・=)
Wait..
"You'll do whatever it takes to be the person she wants you to be" that sounds like a one sided love eh? For me, if you love that person.. you'll going to change by your own will not by she wants. And as for her, she will accepts as you are and embrace your flaws. Love isn't just mere clouds and rainbows but also storms and black and white.
Just saying but anyway looking forward for more.