How can one become religiously committed and strengthen their resolve when they feel weak and in need of a specific person who had a positive impact in motivating them towards commitment, especially after leaving a previous relationship due to its impermissibility?

You both did well to end the emotional relationship, and let this be a sincere repentance. If the girl is religious and of good character, you can propose to her, for the Prophet, peace and blessings be upon him, said: "Nothing is seen for two who love each other like marriage." If marriage is facilitated, then praise be to Allah. Otherwise, each of you must turn your heart away from the other. Your statement, "We will not forget each other," does not contradict repentance. The Muslim's steadfastness in obedience to Allah is obligatory and should not be made dependent on marriage or anything else.