you ever have an intrusive thought that seems so subtle

I wanted to ask if it is possible to purposely think of an intrusive thought and then shifting your mind instantly to something else? Is it still an intrusive thought if you have been thinking of it 'purposely' for a second? I dont know how else to explain it, but it felt like I was purposely thinking of it. Anyone else had similar experience what happened during intimate moments like masturbation I feel so ashamed cuz the thoughts are so bad they're either about family members children and stuff like that it feels like I think it I just want to know if I'm not alone I feel like a monster because it feels like I thought these things or like I did think these things and I don't know what to do I feel so ashamed and grossed I need help I just want to know if anyone had a similar experience to shed light on because I don't know I feel so isolated

for me, it's like there's two folders of my thoughts, 'main thoughts' and 'sub thoughts' and it's like a background voice of my background voice, you know? like so quiet and irrelevant but it's still here and i can try to ignore it but not fully and it feels like it's just really nasty, like it's warring with me, never shuts up and just keeps nagging me with those thoughts

Please how can an intrusive thought be distinguished from our own thoughts ?