Boyfriend messaged other girls in the beginning of our relationship. 2 years later I'm just seeing the emails

In August 2016 he was homeless because his family made him move to another state with no assistance and we would kick it. Tonight I logged into his email and I saw his FB emails from 2016 and my message would say goodnight I love you 💖 and some other girl would message his close to the same time saying. Goodnight I love you too. He was also still messaging one of his exs besides that. 2 years late and been living together for 1.5 he doesn't message anyone else and the messages stopped shortly after August 2016. I'm mad and hurt but he'll probably make it some big deal how he wasn't certain if we'd be together or not and he needed a back up if it didn't work. Maybe not word for word but he did say in the past he tried to stay friendly to people. I've been lied to in the past by another ex