In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatoh
Oral sex is prohibited. It is also against shame and modesty.
Intercourse is a human demand and should be fulfilled in a most respectable manner. Alhamdulillah you regret your wrong. Sincere repentance is never to repeat that sin in future. Whenever you think of that sin, recite Astaghfirullah and ask Allah to forgive you for the thought of that sin.
And Allah knows best
Wassalam
Mufti Ebrahim Desai
Darul Iftaa, Madrassah In'aamiyyah