I'm sorry you're having to deal with this situation.

I probably would answer his last message, the one that said:
and say "No, I don't think that would be a good idea at all. You're married and a lot older than me."

You totally have the high ground here. He is being a creep. If, God forbid, he did show up unannounced, I would not let him in.

I don't have Facebook anymore, but I remember that there was a way to block people from being able to sent you messages. If you don't want to unfriend him entirely, you could block the private messages from him.

I can understand that you might be embarrassed if your mom got involved and got really angry, but she sounds like a good back-up resource to have if the guy keeps bothering you.

As far as my own experiences, I have had experiences similar to this happen many times. (I'm 53.) When I was younger, it would often be married guys who were lots older and they would frequently try to act like it was something innocent.

I think the key for this sort of thing is to trust your instincts, because the guy will frequently try to make you second-guess yourself and try to make it seem like you're making a big deal out of something when "all they wanted was to blah, blah, blah."

You can take the high road and just say "I'm not interested." Sometimes that's not enough and you have to say "I'm not interested in people so much older than me/I don't get involved with married men/I need to ask my mom's advice about this."

This kind of situation is difficult for almost all women to deal with. Anxiety makes it even harder. Maybe it will help if you think of it as a social skill that you will need to know as a young woman. It's really pretty much a formula. There are a handful of things that you can say.

I try to go with the more polite response first and then get ruder as necessary.

I hope I haven't scared you too much.