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I think it is worth communicating with him about the worry of losing him, and he can talk to you about his worries as well. It's not going to guarantee you don't break up one day, but you can create a game plan on what the two of you want from the relationship, boundaries, and what to do if either of you ever finds a conflict/problem with the relationship so it doesn't blow up into an even bigger problem. I'm not saying you'll never argue, but it can help to have a game plan if things happen.

I can't say for sure whether the relationship will last forever. Some people DO meet their soul mates young, but other people have their first loves but they don't last. There's no real way of predicting that. But I can say the pain does get easier if you two do break up. It does take time so don't rush into another relationship or feel like you should have everything figured out right away. Give yourself time to heal and practice self care whenever possible.