Rebuilding trust in a relationship.

I've got a long story. So be prepared for a lot of reading. Let's circle back to August of 2014. I was in the Philippines for vacation. 6,000 miles from home and I was on my laptop. I was talking to my boyfriend one night and he told me he ran into an old friend of his at the gym. Let's call her Josie. Anyways, I had just bought a new laptop so I was transferring data from the old one onto the new one. Anyways, I opened one of the browsers on my laptop (web designer so I have multiple to make sure the code works on all browsers) and when I opened it, my boyfriends Facebook was logged on. I snooped. I shouldn't have but I did. Turns out he messaged her on Facebook and said, "Hey let's go to the gym and I'll pick you up." At the same time, he was also messaging another girl. Let's call her Susie. They were taking hanging out and smoking some pot together. Susie happens to be friends with his ex. So that's what happened. I confronted him about it. He told me that he knew I would be really uncomfortable if I knew that he picked her up. So he opted to lie. As for Susie, he said it was a, "social experiment." He didn't actually want to hang out with her. He just wanted to see if she was going to say anything regarding his ex. I was gutted that he lied. But I forgave him. No questions asked. I simply asked that he not lie to me again. Fast forward to the middle of September when I'm already back from the Philippines. My boyfriend is spending the night at my house. I was doing homework while he slept. I was tipsy. His phone was right in front of me. I snooped. Again. I found out he actually went to go spend time with her and smoke weed with her. He told an old friend of his who happens to be a girl he dated for 5 years or so about it. He told her that he felt bad for lying. But felt that I didn't need to know. I snapped. The day before that was our one year anniversary celebration. I couldn't understand that he could tell me how much he loved me and lie to my face at the same time. I felt destroyed knowing that he had been lying to my face this whole time. Glass of wine in my hand, I told him to pack his shit and leave. We fought. There was a lot of crying on both ends. I asked him why he lied and he said, "Because I'm a coward. I was scared that you were going to leave me if I told you the truth." We did not break up. I told him I am going to forgive you because I love you but I need time to rebuild trust. It's been many months since then, but I still have trouble trusting him sometimes. I sometimes wonder if I'm ever going to be able to fully trust him again.