Clearly you see the route of terrible ideas you keep going down, now you just need some backbone and some willpower to follow through with not making the detour. You need to sit down and decide if this goal is truly worth your time and dedication, if you're not 100% dedicated then you might as well go back to PMO because you will do nothing but fail and be discouraged until you hit bottom.
If you decide this is what you truly want then the answer is simple....STOP DOING THAT. Consider all those sites blocked, you no longer WANT to go there because it only causes problems, no bullshit excuses for yourself, you know you shouldn't for any reason go to any of those sites, period. You need to actively stop thinking about the past and porn in general, by forcing those thoughts out, you increase your willpower and over the course of a few weeks you put that little bitch of a brain into it's place and it will start to behave. You will still have moments here and there but they will be gone just as quickly. End of the day you can only rely on yourself, no one here is going to be there for you in the moment, this challenge is 90% mental, if you don't lock your brain down you will never streak high.