I know lust is a sin but why do lust have a huge hold in your mind

And then when you act out on it you feel 10times as bad as you had it in the 1st place , the thought of it .
I feel the fella downstairs is trying to destroy me with that thought. I rarely act out on it but when I do I feel so crap and guilty over it .
I didnt last for a few years now with something in my system (either nicotine, compulsive eating crap and much more )
I'm striving for perfection is my problem but I'd love to get to that point with nothing in my system or acting out on thoughts in my head .