Cheating?

The past few weeks my husband has been very snappy and short with me, conversation has been cut to slim and I figured it was his new work load overwhelming him so I've been supportive yet gave him a little breathing room. Last night I had to run to the store and we talked about watched a movie once I returned. He asked me to send him the link for the movie so while I was out he could pull it on Netflix. I sent it and noticed his phone didn't go off...so I went and grabbed it to make sure it went through and noticed there was not just one message from me but another from a girl on FB messenger. When I went to click on her message and it went away because before I got home he deleted the app. The message from her said ( are u excited? ) I asked him who she was and why he had deleted it and he just walked off, I then asked him to redownload the app and he stated he wasn't and wasn't going there with me . ( He's cheated on me before) he stated if I needed him to open it then I have trust issues and he didn't believe it was there because he didn't see it....I'm 4 months pregnant with our second and know when something isn't right. Someone please tell me I'm not over reacting