Caught my bf using Grnder

Hello!

For those who don't know, Grnder is an app for gay guys to meet other guys. I had no idea this app existed until I caught my bf using it... We've been together for three years and he didn't use this app before, so when I saw it on his phone I was curious and I had to know what it was. I found out that he had been chatting with a guy and exchanging, racy photos... I was shocked because he had never showed any signs of being bi. I was heart boken, and I confronted him about it. He confessed that ever since he was 13, he never felt like he was completely staright (he is 20 now), but at the same time he likes girls. To me that wasn't the problem, but what really hurt is that he never told me this before, and of course that he cheated. Now he said that he loved me and that he was sorry and all the things guys say when they get caught. I forgave him and agreed to work things out together as long as he promised to be more open about his feelings and in return i would do the same. That was about a month ago... but something still bothers me. Even though he said he never met up with anyone in person I still have my doubts. So how can I adress this with him, and of course how do I learn to let go of my trust issues. 💔 Any advise will be appreciated, thank you:)