Turning off phone plus airplane mode

I just don’t understand my bf of 2 years never did this but recently took it up...and if I’m not mistaken it’s when he had showed me something in his phone while he was drunk and well it involved a different girl.

Since then I’ve been suspicious of him and I’ll look at his lock screen just to see if people message him or any sort of notification however it doesn’t go beyond that because for 1 I don’t know his passcode and 2 he has the Touch ID programmed and either way I can’t see who messages him on Snapchat

So the day everything shifted I had asked him if he’s cheating on me to see what he’d say cause I knew he blacked out and wouldn’t remember anything.

He said no

So then I told him about the girl

And then he gave told me the reasons for doing what he did and i honestly don’t even know what to put it under as...cause like he did it to make this girl happy because she’s terminally ill

But I also know that it does not excuse anything.

Anyways if he really doesn’t have anything to hide why all of sudden turn off his phone and put airplane mode on or just airplane mode. It’s only when he sleeps and he’s a heavy sleeper so nothing really disturbs him.....