Is it permissible to continue communicating with the aunt of the young man with whom the questioner was in a relationship, knowing that this aunt was a reason for the questioner's guidance and that she benefits from her in matters of her religion, even though continuing the relationship might remind her of the young man?

Congratulations on your repentance. We do not advise ending your relationship with your sister, as long as thinking about the non-mahram is merely an occasional occurrence. Strive to divert your mind from him, and fill your time with beneficial knowledge and righteous deeds or permissible recreation. Seek a righteous husband and righteous sisters who can help you remain steadfast. If you fear relapsing into a relationship with the non-mahram due to your connection with his aunt, then cease meeting her and seek help from other sisters.