Am I over worrying?

So, me and fiancé have been together on and off again for four years. We’ve been back together again for a year. Four months after getting back together I ended up pregnant and my son was born in September.

Anyways, we’re 20 now and we’ve been together since we were 16.

When we first got together when we were 16 he cheated on me for about 4 Months with his ex and he did it by doing it over Snapchat and edited her name into one his guy friends so I wasn’t suspicious until one day I opened one of his Snapchat’s from that person and found out it was his ex.

He denied cheating but then a little later in school she showed me texts between the both of them and showed me all of the proof of him cheating.

Fast forwarding to know he won’t let me touch his phone and he changed all his passwords which scares me.

I know we’re not 16 anymore but it’s just because he did it once.

He doesn’t have his license nor a car and works forty hours a week and we live together so there’s not time to cheat in person but I’m just worrying about wether or not he’s hiding anything.