Facebook account switcher is normal. If more than one account has been accessed from a particular computer, and I believe you also have to tell the computer to remember your login info, then you get the switcher. I have a personal account and 2 separate work accounts, and I use the switcher all the time.
That part is harmless.
Now for being hacked (maybe, hard to say) - a lot of what people refer to as hacking isn't true hacking at all. Someone guessing your password or your security question isn't really hacking. So - even if the horse is in the next county, close that barn door now. How? By stopping answering those stupid ass questions about your pet's stripper name or yourself as a meatball. Many of those are harmless on their faces, but they can be used by people trying to pull passwords and the answers to security questions. Pretty standard security questions are pet names, mother or MIL maiden names, streets where you lived, names of schools or teachers, and favorite colors, foods, places, or songs. Any quiz which asks for any of these could
be fishing for something nefarious. They aren't all -- but it does pay to be vigilant.
Now change your other passwords. Seriously. If your information is out there in some way or another, then it may be on a list (most people's information is; this is not a personal failing on your part - it's reality). Using a service like LastPass can be helpful. In the interests of full disclosure, I don't work for them or anything. But people reuse passwords all the time; it's human nature. And with a service like that, you're using just the one password for them and then they automatically create a bunch of hard to crack passwords for you on your accounts and they change them as needed.
Now, back to your pal. I'm not going to get into why it's weird to be pals with a locked-down paranoid. I've got connections to people from high school who are extremely locked down and they have their reasons. The difference is that I also knew them before. But you do you.
Still, their behavior should have been a red flag to you, and I hope that similar behaviors are in the future when you meet people online. There are a ton of people who prey on innocent folks. Even if this person has nothing to do with your situation (and it's possible that they don't, by the way), their behavior spells stranger danger to me, and it should to you, too.
Finally, if you are concerned about passwords being compromised via Facebook, you can always close your account and open a new one. Yeah, you'll have to re-friend people and all of that. But that beats the hell out of identity theft, which I have been through. You don't want to, during Covid and a national reckoning on the role of the police department, be heading to your local precinct house, online identity theft materials in hand (you would go here --> https://www.identitytheft.gov/
) and talking to them about getting a report so you can tell the IRS (among other entities) that your accounts have become compromised.