Cheater or not

So my boyfriend left for a cruise and told me to log into his snapchat to keep our streak alive. During this time, i opened a snap out of curiosity from a girl and turns out they had been making promises to each other to meet and he was saying things like youre so beautiful, i can't wait to see you, I'm so lucky to have you, etc. She is across the country but they used to be friends, 3 years ago, before she moved away. I confronted him and he spilled everything. Of course it was never physical cheating and he said that he would never have done anything or met up because she has changed too much since they knew each other in person. She is now blocked from his life, but i just feel so insecure at times and i still think about it. If i bring ir up i can tell he feels bad and we discuss how i feel and stuff. I just don't know how to feel or what to do! Please help!