Agrees with YGirl on the "name" of the relationship. But to the OP's original question...
It doesn't matter the relationship of the people around. "Common courtesy" dictates that one is not on the phone or texting (which is basically the same thing) when one is eating with others, spending quality time with others, etc. It is plain rude. A single text or a quick call is ok if they are letting the other person know that they are busy and will text/call later. The fact that he couldn't stop himself while he had company who don't know the nature of the relationship is even more rude and embarrassing to you, IMO.
Life is about the journey and not the destination,
so what better way to know life
than to wander all the roads and paths set before you.