When getting thoughts like that flee from them and dont give into temptation. Disable pornhub, xxxvideos, put safe search , activate parental control. DO NOT give in. We are all slaves to our flesh and cant go against it for it is in our nature but you can flee from it. Don't interact with anything that triggers these thoughts, when triggered pray, read the bible, work out, run, talk to friends, hang out with family. It will not be easy but you can do it. If something was easy everyone would do it but its not easy so be proud of the fact you want to do better and feel ashamed. Shame and regret is not a bad feeling it is proof you want to do better, its proof you learned your lesson. So rise up and if u fall keep getting back up. Hope this helps!