Is it permissible for me to check on a girl I loved and communicated with via messages, given that we left each other for the sake of Allah after her family rejected my marriage proposal on the pretext that we are young, and I feel sad for her?

If the suitor is a man of religion and good character, it is not permissible for the girl's guardian to refuse his marriage proposal, due to the saying of the Prophet (peace be upon him): "If someone whose religion and character you approve comes to you, then marry him. If you do not do so, there will be tribulation on earth and great corruption." Marriage is the best cure for ardent love. The suitor should strive to convince the family of the marriage, while knowing that the girl remains a stranger to him until the contract is finalized. She should be treated like any other foreign woman, and it is forbidden to look at her, touch her, or be in seclusion with her. Abandoning forbidden relationships for the sake of Allah will bring good and provision, and grieving over them is from the whispers of Satan.