Boyfriend betrayal

Kinda long so I apologize... Me & my long distance boyfrind have been together for 2 years. He goes to school down south & I go to school up north so we don't see each other a whole lot during the school year. In spring of 2016 I found out he was still talking to his ex gf... "as a friend" so he said. I told him I would appreciate if he would not continue regular communication with her because it made me uncomfortable and he said he would. However, today I found pictures of screenshots of him & his ex girlfriend talking in Jan. 2016. He said how he missed her and how they were gonna go to the zoo together that day and she even called him her boyfriend. I confronted him and he really didnt have an explanation like he claimed, I asked him what happened & he said "I dont know" and tried to say they were from forever ago (which they certainly weren't). He told me he would block her on everything. I'm honestly so hurt and confused right now. He would often say how he was cheated on & how much he hated cheaters yet here we are. I love him to pieces and I want to believe that it was a misunderstanding & trust that hes no longer talking to her but I'm just looking for some advice or encouragement in this time of need... Thank you & hope you lovely ladies are having a wonderful day 💘