What is the ruling on imagining the obscenity of sodomy with a friend while masturbating, and is it sufficient to pray for him, or is it necessary to inform him and seek forgiveness?

What you are doing — masturbating and thinking about immorality — is forbidden. You must address this by striving for marriage if possible, based on the Prophet's (peace be upon him) saying: "O young people, whoever among you can afford to marry, let him do so, for it helps him lower his gaze and guard his chastity. And whoever cannot afford it, let him fast, for it will be a shield for him." Allah has promised assistance and richness to those who marry for chastity, as He says: "And marry the unmarried among you and the righteous among your male slaves and female slaves. If they should be poor, Allah will enrich them from His bounty, and Allah is all-Encompassing and all-Knowing." It is also mentioned in the hadith: "There are three whom Allah is bound to help: the mujahid in the cause of Allah, the slave who wants to buy his freedom to pay his debt, and the one who marries seeking chastity." Please refer to previous fatwas regarding masturbation and the book "Victory over Masturbation." You must also be cautious about associating with the aforementioned friend or being alone with him, and do not tell him what is on your mind, as he has no right over you.