<human>: Couldn't sleep over the weekend so I left him sleeping and went to watch TV, he had left his phone nearby and curiosity got the better of me. 

(Short backstory: He would regularly check his phone when we were together and would get overly protective if I even touched it so I started suspecting something was up.) 

So as I checked his messages, I found that he had messaged about 5+ more women through Facebook with sexually charged messages and pictures of sexual acts from porn or something. The women he was messaging would go right along with it. One of them even proposed to do things in person. He later told her that they should erase the messages. By this point it was 1am and I was so upset that I grabbed my phone, a bottle of rum and walked out. I called my friend and he sorta comforted me but we had to cut it short because he was to be at work within a couple of hours. So (again against my better judgment) I called my ex who lives a couple blocks away from me. We didn't have a horrible break up but we had been together for 4 years so he was the only other one I could trust in. 

I ended up hanging out with him and talking drunkenly. He made me food and gave me plenty of water. My BF started calling me worriedly, I answered and gave him a yelling. I went back home, fell asleep and then talked with him in the morning.

He said he was sorry he was an asshole and that it had nothing to do with me, it was just him being a jerk. He also added that he would never have done anything physically with anyone and it was just all talk. Ultimately, I decided to try to make it work but I feel this vast hole. I'm hurt and can't trust him and I let him know this. He told me he'd spend the rest of his time with me trying to fix this. How does anyone move forward after having this happen?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Caught BF of 5 months sexting other women, trying to move on from it. Don't know how to start. What can I do to begin to trust him again?