Is it permissible to supplicate for one man to love another and for their mutual affection to increase, along with the question of whether this supplication is considered an objection to divine decree or brings evil, and are there specific supplications or methods for its fulfillment?

It is permissible to ask Allah to make people love you. Abu Hurairah asked the Prophet, peace and blessings be upon him, to pray for him and his mother, that Allah would make them beloved to the believers, and the Prophet responded to that. Similarly, Ibn 'Umar used to supplicate with a prayer like this. It is important to strive for mutual love for the sake of Allah, as it is one of the highest ranks of faith and leads to attaining Allah's love and winning pulpits of light on the Day of Judgment. Among the means of gaining people's love are spreading peace, being ascetic in this world and in what people possess, and giving gifts. It is recommended for one who loves someone for the sake of Allah to inform them of that.