Fear of abandonment

I don’t know what to do anymore, I’m completely losing my mind. There are too many big changes occurring in my life next month and the anxiety of it consumes me. First, I’m moving back home from university. And second my boyfriend is moving out of state for med school. The issue is that ever since my boyfriend told me his plans about moving for school I’ve been freaking out because I feel like he’s going to leave and abandon me. We’ve talked briefly about doing long distance but I just have no clue how long we’re going to be able to make that work if at all. I just feel like I need answers and I’m not getting them anytime soon. How do I stop obsessing over the future and thinking of all the million ways things could go wrong? I’m struggling to comprehend that this might be it for us..and if it comes to that there’s no way I’m going to be able to get past it, I will be crushed and devastated.