Thank you for writing. Your experience with the movies tells me you have a strong visual memory. This is both a gift and a problem. Once you see something that you experience as emotionally powerful, it’s difficult for you to let it go. (Often people who are very successful photographers, artists, writers or film-makers share this tendency.)
No. Don’t even think about ECT. It is not an appropriate intervention for this problem and, as you fear, it is not selective. You would lose memories you want to keep.
I hope you have already stopped adding disturbing scenes to your memory bank. If not, stop it. You already know that it makes a problem for you.
As for “erasing” the bad memories, I have a couple of suggestions:
First, think about some very positive and powerful memories. If you don’t have some, go make them. Identify at least 3 such positive memories to use as a support when you are pulled to the negative ones. Whenever the negative memories start, get very quiet, take a deep breath and shift your thinking to focus on the positive ones. Engage every sense. Remember what you saw, smelled, heard, and felt both physically and emotionally. Immerse yourself in those positive memories and let yourself re-enjoy them.
Then, start a practice of mindfulness. There are many sites on the internet to teach you how. Mindfulness helps you stay in the present and let go of disturbing thoughts. With practice, you’ll be able to relax and let go of the memories that trouble you.
I wish you well.