Talking to Your Kids About Sex by Dr. Laura Berman
The First Intimate Relationship

Most parents will experience their child going through a variety of crushes and casual relationships, so it can be difficult to know when he has actually moved on to a more serious relationship—and everything that might entail, including physical and emotional intimacy. The best barometer you have to judge your child's relationship is conversation. Talk to him about his relationship, and try to ask questions that will illuminate the seriousness of the relationship. Your child might be hesitant or shy to speak at first, but the more you seem genuinely interested in his relationship—as opposed to anxious or judgemental—the more he will feel safe sharing these personal details.

For example, you might ask: "How long have you and Kate been together now? Almost a year, right? That's a long time. Do you ever talk about the future? Do you think you will try to apply to the same colleges? If you go to different schools, will you try to maintain a long-distance relationship, or do you think you will break up?"