In actuality, Jim was just plain curious. He hadn't heard anything about their relationship so far and he was just plain curious about how that worked exactly with Spock's no-touchy bubble. He figured it had to be some intense telepathic sex, if that's even what happened.
"I'm just curious how things are going. Everyone knows that you two are together but we never hear any details. We're friends now, right? Come on, spill!"