long term relationships advice

i’m currently about to make a year with my bf, come december. i love this man so much and want it to work. sometimes i feel like i am controlling only bc he has given me reasons to get that way & the trust issues he has given me. we are both 19 with cars and live together with a dog. i need advice on long term relationships. one of my biggest fears is getting cheated on by him. so i feel like i get controlling sometimes. he doesn’t complain but he has like twice before about me feeling upset bc he wanted to be with his friends alone. in my head i’m thinking like why i can’t come with you ? i felt a type of way. idk where i’m going with this story but how do you guys keep your relationship strong after many years of being together. have y’all ever stepped out on each other? loyal the whole time, what problems do you face, how do y’all deal w the attachment etc.