A question

Okay, so I asked my bf to stop looking at nudes/porn gifs and just to stop actively seeking them out. He said he will stop, but he had been looking at them again. I do things for him, like not smoke or do drugs, which I'm okay with doing.

It hurt to know that he went back on his promise. I'm not a very trusting person, and some of the trust I had with him went away.

What are some ways to earn trust back? And how does one go about knowing that he did what he said he wouldn't do anymore?

Thank you!