Is it permissible to inform a girl of one's feelings of love and intention to marry in the future, while observing the Islamic legal guidelines, given circumstances that prevent marriage at present and after six years of concealing these feelings? And is there a supplication to purify the heart from this love and replace it with the love of Allah, His Messenger, and the homeland?

If you are able to marry, then propose to her. If it is made easy for you, then praise be to Allah. If it is not made easy for you, then turn your heart away from her, and be sincere in your resolve with Allah, and He will heal your heart from her love. There is no harm in supplicating with what has been reported in the Sunnah, such as: "O Allah, I ask You for the performance of good deeds..." and "O Allah, grant my soul its piety...".