I'm confused. And scared.

So anybody know about how facebook is no longer letting you read messages through browser, you have to have the app? Well I have an old facebook that I only get on to talk to one person because I don't want her on my other profile. So eventually my old facebook stopped letting me read messages so I had to open them through the app. U discovered if you have multiple pages the messanger app let's you easily switch between those profiles. So this is just the info I know on the app. Here is the story and why I'm nervous....

I was laying down trying to sleep and for some reason I hate that little notification light that blinks on some cell phones. My fiances was blinking so I grabbed it to swipe of the notifications so it'd stop blinking, thinking it was just the post I just tagged him in. Well, it was his old facebook that he has been telling me for weeks that he can't access anymore. I tried to click it but it said I needed a password. It showed the account was last active 14 hours ago and there was a message. I don't feel right about this. He has no reason to lie. I am pretty sure he lost access to it before the Facebook app thing made you switch to messanger so how would it show up on his messanger app. Is it possible? I sound naive but I'm so confused.

I woke him up at 4 am to express my concern and he calmly told me he doesn't know his password. He even told me before it's possible his old best friend changed it. I mean he was calm and sounded upset that I didn't seem to trust him.