How can I sincerely repent from conversing with youth, and what are the signs of my repentance being accepted and Allah being pleased with me?

You must sincerely repent and strive against your soul to remain steadfast by being conscious of Allah's watchfulness, avoiding being alone with the internet, associating with good people, and filling your time with acts of obedience. If you fall into sin after a previous repentance, repent again and resolve not to return to it, for that does not invalidate the previous repentance.