I've been through the exact same thing. Me and my boyfriend were only 16 when we broke the law of chastity. It only happened once and we kept it a secret. Though, my mom, who knows everything found out first. I was not a member at the time and neither is my family, so my mom was a little more understanding and only "grounded" me for two weeks. Eventually my boyfriend's parents became suspicious and the guilt finally made him confess. His parents at the beginning told him we could not be together ever again or at least see each other any time soon, and I was heartbroken. But we stayed in contact and I went to church every Sunday to see him. Eventually the Bishop told his parents that they were a little harsh and that needed to lighten the punishment (my boyfriend is there first child so it was their first experience with anything like this). We slowly gained his parents trust back and after a few months our relationship had returned back to normal. And while my boyfriend was unable to pass the sacrament, after 8 months he was able to take and pass the sacrament.
During that time I was not a member, and did fully understand the seriousness of the law of chastity. About a month ago I was baptized. I have repented and I have been cleansed of those sins. Now that I constantly have the Holy Ghost, I found myself being smarter with my decisions when it comes to be physical and the situations I put me and my boyfriend in. When I do have those "desires" something stops me from acting upon them. My advice is listen to the Holy Ghost. That constant whisper is something that can save you from grave sins.