Is it haram to read about sex just for fun?

When I had free time I would love to read, but due to COVID I can't access any 'real' library books, so I just started reading online books. After some time in reading though I started reading characters having sex, I didn't know what it was at first but after some research I started to realize what is it. I try not to read but it's just so addicting, I really am trying to stop because I don't know if it's haram and I want to stop but I just can't. Every time I try blocking that book it comes back into my mind and I read it again. After I read it I feel regret and ask for forgiveness. I always wish I hadn't read it but once again it'll come into my mind and I'll read it and therefore the cycle restarts. I don't know if it's good or bad and I don't know how to stop. What should I do?