How do I build trust again?

My boyfriend and I have been together for almost a year now and he’s amazing so far. He’s very caring and it doesn’t take much at all for him to pick up on my emotions, he’s very in tune with me. But every once in a while I’ll catch him in a lie and at first it wasn’t a big deal but recently he hurt me really bad when I caught him looking up girls he knows and buying sexual content from them. From my understanding he doesn’t talk to them and they don’t know it’s him buying their content but it still hurt me more than anyone else ever has. For context purposes our sex life hasn’t really been the best as there is something wrong with my hormones that has made my sex drive almost non-existent, while his sex drive is really high. So I can understand his sexual frustration with the situation but that doesn’t change how he kept things from me and continued to try to cover his ass until I uncovered it all myself. I talked to his sister who is much older than us (I’m 19 and he’s 20), and she reassured me that he’s very obvious with how much he loves and cares about me and talks about me when he’s around them which made me feel much better. I ultimately came to the conclusion that he’s still very young with a lot of maturing to do and he’s bound to make some mistakes and not really understand how that would effect me sometimes. I don’t feel in my gut that he would cheat on me but other than letting time run it’s course I don’t know how I can get my trust in him back or if it’s ever going to come back like it was before. It’s hard to be confident that he’s not going to do anything that will hurt me on purpose even though to the core I don’t think he will. I can’t seem to stop the anxiety that washes over me. How do I help this?