I have evil thoughts and can't control them. serious answers please. Jonah. 17. male?

So basically if I see something gruesome in a movie like someone being tortured or killed sometimes I will picture people I love in my life having that being done to them by me or something else messed up. I know this isn't me and has never happened before. so yeah that's a glimpse of the evil thoughts then also I have lots of sexual thoughts and I have a gf and sometime ill have them when were making out.. ha it's terrible cause I know they're bad thoughts and I'm not thinking of them cause I'm a bad person. It's almost like I think of them knowing they are bad then I think why am I thinking about this? then that thought continues to stay in my head and cycle and I cannot stop it and idk what to do sometimes.... especially if i told these people about the evil thoughts and i did tell my gf about the other part and she was not too happy.. i recently told my gf i was unfaithful to her not cheating but something somewhat similar and i feel this triggered some of the thoughts cuz i get down on myself and dont think highly of myself because of it and before that happened i would never think like this. is it possible this is what triggered them? cause i think of the things i ****** up on then i think of a bad sexual thought and i would think this would be bad of me to think but I STILL THINK IT and cannot stop it and they keep coming. cycle cycle cycle etc... please help