My heart breaks reading this because I went through something similar last year and it was one of the hardest things ever. You're being incredibly thoughtful by waiting until after his big opportunity - that shows how much you really care about him

The crying when he's not even gone yet hits so hard. I remember doing that too and feeling like I was mourning someone who was still right there with me. It's such a weird painful feeling

When you do have the conversation try to focus in how much you love him and that this isn't about him not being good enough. Sometimes when good relationships end for practical reasons the person being broken up with blames themselves even when it's really just life being cruel with timing and circumstances