Breaking.

He thought a lot, about the best way to end his life. The way that will be the least burdensome for the others, that is.
He doesn't want to traumatize his children with such a thing, nor to give TiHao a hard time. Plus, if he just died like that, he wouldn't achieve anything of what he wants the most: fix his mistakes.

He had already made a plan, about it, in case he wouldn't manage to find TiHao's powers with all his efforts. Qi's harshness just pushed him towards plan B, demotivating him from continuing to try. He clung to the hope that, if he had found TiHao's powers, everything would get solved. His pain would go away and he would just be like before.

He has taken the decision and he is sadly at peace with it. All he needs is to find a way to make his plan possible, since he intends to go back in time to kill the WonPil of that time, consequently disappearing too.
He chose carefully the moment he thought to be the most appropriate: few days after WonZi's birth. That way, he wouldn't cause any of his children not to be born and WonZi would be too little to understand what happens around him, or to feel the loss.
He couldn't do much to spare the others from the possibility they would suffer from his death, but at least he can count on the fact that the present versions of them will have overcome everything.