I've been there too, OP, but I was the person dumped because my partner wasn't ready for things to get serious. We didn't have the grad school angle, but were fresh out of college and starting our lives and it was too scary for them to be that serious. I took that breakup hard, mourned, and went total no contact. I dated other people, moved cities, got a new job, was having a really good life, but my new partners weren't my old partner, and even after 2 years, I still missed them.

They still missed me too. We ended up reconnecting and discussing things deeply before getting back together. Now we've been together for years, live together and are planning a wedding. But it was hard. It took me a long time to trust that they wouldn't just up and leave again. But, we're more honest with each other than we ever were before, and are stronger for it.

Getting the trust back will be hard, but if the relationship is worth it, you'll work through it. If it's not worth it, then you'll need to move on. But that's something only you know.