How do I learn to trust? LDR

My boyfriend (18) and I (17) met the last month of freshman year of highschool, became friends, fell in love and became a couple the summer of our sophmore year. During that summer, he was visiting family in China so the distance and inability to talk much was hard. When he returned, we began our junior year together only for him to move 5 months of being back in America to a different town 40 mimutes away. This summer, he has moved again and now he is 3 hours away. This constant distancing has been really hard and even though we are both our first loves, first kiss, first EVERYTHING, we really want to have a future and family together and we don't want to be with anyone else. However, I suffer from severe abandonment issues and anxiety as well as depression and am constantly worried that he will cheat on me. In a LDR, trust is essential. I have no reason to not trust him, I know that he loves me, but how do I learn to trust him within myself? What are things that I can do for myself and for our relationship to keep the trust strong as well as our relationship?