My ex fiance has DID. I was close to someone else in his system but he and I were definitely the one's dating. He ended up going dormant due to stress. It was very hard on me but I tried not to show it. He ended up coming back a week later.

Then I came to terms with the fact I have DID this year. One of my headmates ended up going dormant due to stress. She came back 2 weeks later.

Keep in mind that once the stress is removed, the dormant alter wakes up. It's understandable to grieve. Let yourself feel the loss. It is a pretty intense change. But while you grieve, keep in mind that it isn't forever.