Narrated Abu Huraira:
The Prophet (sallallaahu alahyhi wa sallam) said, "Allah has forgiven my followers the evil thoughts that occur to their minds, as long as such thoughts are not put into action or uttered." And Qatada said, "If someone divorces his wife just in his mind, such an un-uttered divorce has no effect.:
[Sahiih al-Bukhaari Hadiith No. 5269]
The best guidance is that of the Messenger of Allaah (sallallaahu alahyi wa sallam).
There is your answer.
I remember I suffered from such horrible evil thoughts as you have mentioned. I suffered them for a straight year.
Don't utter what you think and do not act upon it. You will be fine.
And be happy that the devil can only do so much as incite evil thoughts and nothing more. Read the following hadiith
Narrated Abdullah ibn Abbas:
A man came to the Prophet (sallallaahu alayhi wa sallam) and said: Messenger of Allah! one of us has thoughts of such nature that he would rather be reduced to charcoal than speak about them. He said: Allah is Most Great, Allah is Most Great, Allah is Most Great. Praise be to Allah Who has reduced the guile of the devil to evil prompting. Ibn Qudamah said "reduced his matter" instead of "reduced his guile".
Ibn Qudamah said "reduced his matter" instead of "reduced his guile"
[Sunan Abi Dawud]
You are not alone. Others have suffered with this as well. Keep holding on tight to the rope of Allaah. He will deliver you from your problem. Also consider reciting the following
Abu Huraira reported Allah's Messenger (sallallaahu alayhi wa sallam) as saying:
He who uttered these words:" There is no god but Allah, the One, having no partner with Him. Sovereignty belongs to Him and all the praise is due to Him, and He is Potent over everything" one hundred times every day there is a reward of emancipating ten slaves for him, and there are recorded hundred virtues to his credit, and hundred vices are blotted out from his scroll, and that is a
safeguard for him against the Satan on that day till evening and no one brings anything more excellent than this, except one who has done more than this (who utters these words more than one hundred times and does more good acts) and he who utters:" Hallowed be Allah, and all praise is due to Him," one hundred times a day, his sins are obliterated even if they are equal to the extent of the foam of the ocean.
[Sahiih al-Bukhaari]
Arabic to be recited
لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ وَهُوَ عَلَى كُلِّ شَىْءٍ قَدِيرٌ