D.B.
Try to ask him questions that cannot be answered with "yes" or "no" or another one-word answer - "What did you do in school?" is better than "how was it".
Kids this age are naturally reticent as they start to experience feelings, body changes, and social situations that are new and confusing. "Dating" at this age isn't really dating - they just say they are "going out" which means they text each other for a while. When they run out of things to say, they "break up".
You might ask him what other kids mean when they say "date" - don't ask him about HIM, but what the trend is. It's less personal and he may give you some info. If you don't pry into his life and don't shut him down with any criticism, you stand a better chance of getting SOME information. But it's hard, especially when they tell you things that sound a little upsetting.
You are very smart to only let him "date" at public locations with a group. I'd stick with that for a number of years. That's how it works around my town. If parents give in sooner, it's a mess. And kids kind of rely on parents to restrict them so they don't get into situations they cannot handle.