To ask you to put yourself in this situation and tell me how you would genuinely react?

[ProverbialOuthouse]

You start a new hobby. Let's call it karate.

First couple of times it's fine but then instructor starts saying he's really glad you've joined his club and he can see the two of you becoming good friends. He goes on to ask if you can keep secrets but does not tell you any, just says it's good if you can keep secrets. Over the weeks he goes on to say stuff like "I feel we have a great connection, I see you as more than a student, more like a close friend" and "remember when I asked about secrets? Does it still stand?" Etc etc!!!! Creeping me out now. He's a wrong 'un isn't he?

Yes, he sounds a bit creepy.

I'd get him to tell me all his little "secrets" and then shop him to someone. Just walking away doesn't seem enough because if he's talking about Thailand like that then he's definitely talking about underage sex.