My T was treating me for GAD. Whenever my husband would go away on a business trip and leave me alone for a few days, each night he was away I'd have to stay up until 3:00-4:00 a.m. by which time the "robbers" would have all gone home to their own beds

I was quite sure someone was going to break in and "get me." Another time, in the snow, I was quite sure I saw footsteps under the windows, amongst the bushes.
It took a zillion years but I finally worked out that it was easier for me to be scared of vague robbers who never came (and weren't likely) than to deal with the "abandonment" of my husband being away from me on a trip and how much I missed having someone/him with me. What began to work over a lot of time was to leave the lights on in the living room (like they were when he was home; I'd go to bed an hour or more before he did and he'd be out in the living room watching TV or reading, eating his late night snack, etc. and it was comforting to "know" that) and that was enough. It looked/"felt" enough like when he was home that I could go to sleep gradually sooner each trip until I would only read until Midnight or 1:00 and, when I was tired/sleepy, instead of making myself stay awake I'd go to sleep (but sleep a bit more lightly/uncomfortably). The footprints in the snow under the bushes I finally realized were snow dropping from the bushes in footprint-like clumps
What is hard to think about/face when you're alone? Can you be "distracting" yourself from missing someone or being alone and "in charge" (one of my big things when I'm scared, "who's going to take care of me????")?