Well, yes, it is fine for William and Jecca to hang out as long as Kate is ok with it. From what I have read here, from others' posts, it seems that Kate is ok with it. So I think it is fine. But if he was doing it and it was hurting his girlfriend, yet he persisted, knowing it hurts her, then it would be mean. But that doesn't seem to be the case. Nor do I believe William would ever be so cruel.
About this story:
http://www.theroyalist.net/content/view/623/2/
If this is true, it's great news! Kate and Jecca becoming friends, that would be fantastic. If it's true, maybe they went to Eleuthera, that is a Mountbatten favorite and it's in the Caribbean.