What is the ruling regarding my remaining with my wife after discovering that she used to speak with men online and on the phone in her youth?

Prevention is better than cure; therefore, you should keep social media away from the home. If its presence is necessary, then regulate and monitor it. What your wife did was a slip, in which Satan, idleness, and the love of experimentation entrapped her. She must repent from it, resolve not to return to it, and distance herself from its causes. We advise you to forgive her and not hold her accountable for what has passed, and to be keen on blocking every excuse that led her to such communications.