I'm around your age and I understand that feeling of relationships constantly being on your mind. Dating, as teens, honestly doesn't mean much. If you think that coming out at this time is maybe not safe or you're currently in a bad situation, then hold on a bit longer. But if you're sure, maybe start by telling a very close friend. It's always easier to tell your friends stuff than your family. The saying "blood is thicker than water" doesn't mean that your relations with kin should be stronger than all your other relations (friends, partners etc.). The full phrase is "The blood of the covenant is thicker than the water of the womb." Which means the opposite; your relation with the people you CHOOSE is stronger than your relation with blood-related family. Also, telling maybe one or two people who are close to your heart can really help you through coming out.Now getting your mind off relationships. It isn't too hard. I recently had some trouble with this exact problem and what I did was surround myself with hobbies. Surrounding yourself with things you love to do will slowly ease your mind off of relationships, dating etc. Pick up a few old favourite books, go for nice long walks in the fresh, crisp morning air, try new sports. These all helped me quite a lot. But no change is done over-night. Everything takes time. There is no truer phrase than "time can heal anything". Working against your mind and your thoughts can be pretty rough. But participating in physical activities that can slowly transition your brain from thinking about relationships to thinking about the activity at hand. I recently picked up a few new sports and it has honestly helped so much.I wish you all the best in this part of your life! Remember that it will be hard, it will take time. Do your best!!
