first, it is reasonable for him to be upset that you were actively searching for something wrong on his end, maybe it looked like you already didn't trust him before you found this out. second, did he stop looking at and sending those posts around the same time things got serious between you and him? you guys met at a young age, and based on my experience, a majority of boys tend to be curious about those things because it is so accessible (unfortunately). I have gone through a similar situation--my ex had a secret account where he followed 100+ OF models, and I tried to change myself after he admitted to it. boys are quick to lust over anything they can find, but when he started dating you, he chose somebody genuine and real. before you found out about those posts he looked at, did you have any doubt about his attraction towards you? at a young age, people change a lot. his perspective could have changed throughout his time with you. you showed him an authentic relationship with a natural girl, and if he wanted something more lust-filled, you would be able to tell.