In the list of who's done what, I get notification that I've "messaged" someone when I haven't actually sent them a message. Does messaging include adding someone to "Favorites" and simply viewing his profile? (Sorry, I'm new at this.)

If you added them to favorites, then yes, it does notify the other person. Unless you are on stealth, then it shouldn't

Viewing a person's profile doesn't send an email, but it does show on their end that someone viewed them.

Kim
Site Moderation Team

One more question: Should I more or less write off people who haven't accessed the site in a month or more? Unfortunately, they seem to be the ones that interest me the most.

that all depends on you. It could be that they aren't on the site for lack of receiving emails or many other reasons.

I promise this is the last question: Someone I added as a favorite subsequently got that news (check by sent mail) and viewed my profile, but when I clicked on his photo it said that his account was "deactivated." How is that possible?

That means the user himself de-activated. Sometimes they decide to leave (for a short time or for a long time)