Relationship Advice

Me and this guy have been together for 4 months, it’s going pretty good and I love it and I love him a lot. He wants to last with me, like get married and stuff when we’re older and I do too but, I’m scared we aren’t gonna last, Ive been so focused on when we may or may not break up it scares me and makes me over think, I’m so grateful for him and he makes me the happiest person alive with his personality. Can I get help with someone who has experience ? I want to believe we can be ‘ middle school sweethearts ‘ ( im 13 ) help ? 🤭