I Have No Idea What To Do At This Point

This seems like something easily solvable but I just don't know what to do. 

Basically, my boyfriend confessed a couple days ago to "looking at other girls" as like interested. After he told me this he said he did this "a year ago" and has stopped in that same timeframe of a year ago. He says that he never wants to break up with me and he loves me a lot. That he doesn't want to be with anyone but me. He also says he didn't cheat on me in any way and he didn't try to talk to anyone and he isn't talking to anyone. That I can go through his phone to check but I don't want to go through his phone because that's a lot. 

Right now, I have an inner war in my head going on. On one hand I want to break up with him because how can I trust him after this. Like am I not enough for you? What am I doing that makes you want to be with someone else? Am I not pretty enough for you? Am I not doing enough? Like why did you feel the need to do that? Also why did you wait a year to tell me? Were you talking to someone? Are you still talking to someone? Did you try to get with someone and it didn't work out?

On the other hand I want to forgive him because in a way this is him trying to move our relationship into a "more mature,"  long term relationship instead of a short term, immature one. 

I love him so so so so much. Like I see my whole future with him. I don't want to let that all go. We've been together for almost 3 years so I don't want to quit on that.