How do I distinguish between harmless flirting and "affair-flirting"?

A man in his 50s is kind of flirting with me. He deals with a lot of young people due to his work, that's why I always thought that's just the way he behaves.
But now I'm starting to wonder whether his flirting is really "harmless", meaning just for fun and a way of communicating with the younger generation, or if it is him trying out how far the girl will let him go.

Some examples of what he has been doing over the past year are:

touching me whenever possible: shoulders, back etc.
asking whether I have a boyfriend
coming very close to me, persistently
complimenting me
telling jokes, teasing me
reading out stories to me
calling me beautiful
his hand "bumps" into mine
checking me out
bragging and trying to make laugh
imitating my humour
giggling at what I say
hugging me carefully
telling me I mean something to him
observing me and commenting on it
getting nervous around me
smirking when I do something he seems to find cute
offering his help

You see, I'm confused as to whether this is his way of being friendly or something else. I never thought that way, but each time he comes extremely close to me or basically hovers over me when he shows me something, I'm a little irritated and don't really know what to think.

What are your opinions on this?
Thanks a lot! :)
How do I distinguish between harmless flirting and "affair-flirting"?
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