I agree that you should try to move on from this for good reason that you mentioned.

He's been consistent, he doesn't talk about exes and doesn't ask about yours so you know he just doesn't do that sort of thing. Seems pretty consistent with the fact that it's cultural too. You mention the contrast in what he'll be open about and spoke as if this is a negative but I don't think so. That speaks also to his consistency. If he was open with talking about some of his exes and just not this one, I would begin to worry but that doesn't seem to be the case. The fact that he simply said "not really" was also just related to the fact that he only said as much as he had to, he just answered your question and that was that, well, again, because he just won't go into detail about her.

From what you've mentioned it doesn't sound like you have evidence of them contacting each other at this point either. It was simply "liking" a picture related to him or of him and that, to me, isn't the equivalent of them really keeping in touch anyway.

Trust me, I'm like you, if it happened to me, I would probably be on here looking for reassurances, as I have a very sensitive radar when it comes to other women when I'm with someone, and can be quite insecure when my SO is keeping in touch with exes.

Hope this helps *hugs*