Do I tell my best friend I'm in love with him?

You have to follow your heart sweetie. Sometimes the best relationships happen between people who have been best friends for years, but it takes some time to realize the feelings. Its seems Justin just wants you to be happy, i dont know if you should tell him. You need to realize first without thinking about Justin for a second, if Derek is the person you could see yourself being with for a while or forever, if he treats you right hun you need to be with someone that is like that. Maybe you should just talk to Derek and let him know that you know Justin has been your best friend forever and its kind of ridiculous that he is wanting you to chose. I wouldnt tell Justin just yet. make sure you know what your doing. but you do need to talk to Derek