Zlat said it the best, stop visiting porn sites, at least on that browser and even then it may not matter. Whatever you are looking at and viewing the most on your browser will be what the ads display. I have literally done a search on a specific topic and gone to my phone and found an ad in my email or on a website immediately after. I would suggest using two different browsers or at least two different google accounts. It's likely that Google keeps track of activity on the devices used, as well as the exact details of the sites you search and visit. They also use your account profile to keep track, as well.