Try starting with some humor to break the ice for a real conversation. When you are talking about the logistics of your trip, at an appropriate moment in the conversation throw in a comment like “When I get back, I’ll tell you all about what happened during the week. But I’m sure the stories you’ll have about what you did with your boyfriend will be much more exciting.” Just a thought. It always seems easier for me to introduce a more serious discussion with a little suggestive humor. Her reaction will help you judge whether it is a topic she is able to handle at the moment. You may have to say something of the sort several times (on different days) before she takes it up. The second time you joke about it, she’ll know there is more than just a laugh behind it.