Engaged and I think he is cheating

I want to know if my fiancé is cheating before we get married June 25.  And I say that because he jus got a iPhone a couple weeks ago... And I have one too. But his phone does these alerts but u can't see them. The he had before was pretty basic and He wasn't into the social media or anything. But when he got that iPhone.. It's been weird. He on fb. Instagram. Snapchat. Kik. N now he so protective over it. U know how he can hide yo messages where they can't be seen? Yea. So that's what made me question. He got a iPhone 5s. N I'm tryna figure out his code. Like I need to know before we get married. I asked him couple days ago, and he said "no. We bout to get married. Have a baby." Because im 6 wks pregnant.. We going thru premarital counseling too but I jus have my suspicions. What I do?