How do I deal with sexually intrusive thoughts?

I have this constant fear and delusion that one of my parents is going to molest/sexually abuse me, it never happened but I always have nightmares about it that seem so real. In addition, I have these intrusive thoughts about having intercourse with said parent and it's driving me crazy and giving me distress, sometimes it gets in the way of doing regular activities because it's constantly in the back of my mind.
Asked by plant123
Dear plant123,
Thank you for your message. Thank you for your trust in sharing with me the burdens that you have been carrying and allowing me to understand the pain that you have been going through.
I understand that at this very moment we are overwhelmed by all the wounds that we have endured and felt the weight of all this pain on our shoulders. To begin with the conclusion, things will get better and the fact that we are feeling all this intensity of pain is because our body and soul are trying to heal. We are often aware of our wounds when they begin to heal. Part of this process is called "flashbacks" where we are triggered by present events or interactions that remind us of our past traumatic events, even though in reality we are safe from harm at the moment. Our brain has yet to catch up and is playing tricks to make us feel that we need to run away. It is our survival instinct and it takes time for us to get used to feeling safe again, having been through traumas.
When it comes to how our past traumatic experience influencing how we approach relationships now, it might be important to actually be dealing with the flashbacks as you said so that we would feel safe with this relationship.
Here is an example that can introduce us to understand more about flashbacks and what we can do with them:
Peter spots his friend Hannah at a party. She has her back to him, so he touches her shoulder and greets her. Rather than turning and answering, she goes rigid for a few moments, then takes a deep breath and asks him not to touch her by surprise again.
For Hannah, the unexpected touch triggered the sensation of being violently grabbed on the shoulder during an assault. She felt a spike of panic as if she were back in a dangerous situation. She was having a flashback, re-experiencing a traumatic memory.
Narrative and traumatic memory
Our nervous systems store ordinary, non-overwhelming experiences in the form of narrative memory, including a sense of time, place, and ourselves as narrators. When a narrative memory is remembered, it is clearly in the past tense.
Back when Hannah was being assaulted, her body was focused on survival, too overwhelmed to create narrative memories. Her nervous system stored traumatic memories instead: fragments of raw sensory data without the anchors of time, place, or narrator. Traumatic memories are remembered in the present tense.
Traumatic memory: Pressure on the shoulder, sudden jerk off-balance, close-up of a milk carton, terror, draft of cold air, anger, beep of a cash register.
Part of the healing process
Flashbacks are one of the hallmark symptoms of PTSD (Post-Traumatic Stress Disorder), where they are described as intrusive sensations, emotions, and reactions from the past which impinge on a trauma survivor’s present-day life.
Recently researchers and therapists propose that flashbacks are part of the healing process for PTSD, rather than a symptom. Each flashback helps defuse and integrate raw traumatic memory into less charged narrative memory.
The key is to experience the distress of the past within the safety of the present. If past distress entirely blocks out awareness of present safety, the effect is re-traumatizing rather than therapeutic.
Recognizing flashbacks
When a traumatic memory fragment is recalled, the lack of context makes it hard to distinguish from the current sensory experience. Some flashbacks contain emotion (terror) or internal sensation (shoulder pain) without accompanying images or sounds.
Some signs of a flashback are:
Strong reaction – a response that is unexplained by current events
Timelessness – a sense of “always”, “never”, or “forever”
Disorientation – confusion about current dates, times, places, or people
Overwhelm – feeling helpless, powerless, or trapped
Changed self-perception – feeling smaller or younger
With practice, you’ll become familiar with your own internal signs of a flashback and come to recognize them more quickly.
Responding to flashbacks
When you notice some of the signs of a flashback:
Notice what you are experiencing. As you witness it, it begins to heal.
Acknowledge your response. Whether you are responding to the past or the present, your emotions and reactions are real and need validation.
Ask yourself if it is old or familiar. Sometimes simply naming a flashback reduces its intensity.
Orient to the present. Look around, say the date, say your age.
Ground yourself. Take a deep breath, stamp your feet, drink some water.
Remind yourself that it ended. Whatever you are remembering, you survived it, and you are safer now.
Take gentle care of yourself. After the flashback ebbs, you may feel raw and fragile for a while. I call this a flashback hangover.
Managing triggers
Peter’s touch on Hannah’s shoulder was the trigger: a current sensation, emotion, or thought which leads to a flashback. Triggers are usually similar to traumatic memory in some way, but the connection is not always obvious. The time of year, a faint scent, or a fleeting thought could be triggered.
When you are experiencing a lot of flashbacks, avoiding triggers helps establish safety and gives you a chance to rest. When you are feeling calmer and stronger, you can gradually expand your horizons and re-introduce some triggers. Establishing a foundation of safety is crucial for healing.
Healing in action
Since she’s had a lot of practice, Hannah could observe her intense reactions, name them as a flashback, and remind herself that she was safe at a party. As the reaction ebbed, she could take a deep breath and set a boundary with her friend to avoid that trigger in the future.
By experiencing the distress of the flashback within the safety of the party, she has taken another step toward processing traumatic memories and integrating them into narrative memory: Two months ago, I went to the store to buy milk, and someone grabbed my shoulder.
Take pride in your process
Flashbacks can contain wrenchingly painful material and interfere embarrassingly with daily life. At the same time, they are a sign of your body’s wisdom reaching for healing. Remember to take pride in your survival, your current safety, and your strength as you confront and heal from past trauma.
Please also note that this is a process that requires lots of patience from ourselves. It’s all about trying and practicing these techniques whenever we can until they become a part of us and we can count on using them naturally. 
That being said, it takes time and practice before we feel confident and comfortable. Therefore in the meanwhile, it is crucial for us to continue practicing self-compassion, being gentle and kind to ourselves, and walk in this journey of healing slowly, one step at a time.
Please let me know if this is helpful and I’m looking forward to hearing your thoughts,