Leonel didn't regret his actions earlier.
His regret had become a recurring event with him. He would make a mistake, acknowledge it, then move on. Over time, he wouldn't make the same mistake again, but that wouldn't stop him from making more and continuing to regret them.
For all intents and purposes, this was another mistake. Leonel didn't consider the fact his Soul Force could ever run out. This was only natural. He had become so used to using his Soul Force with impunity, he didn't even think reaching his limit was possible.
It seemed impossible to him. After all, he had a mind with the capacity of a Fifth Dimensional entity even if he was lacking in the power. Running out of strength while battling within the Third Dimension would seem ridiculous to anyone.
However, this was the reality before Leonel…
Yet, he didn't regret it. In fact, it was something that filled his heart with anticipation and fervor.