"Does anyone else understand what this is like? Please tell me I'm not alone."

I understand this so well, and no you are definitely not alone. I am finished with therapy, and do not have a SO, so I still use my therapist as that go to person in my head. It doesn't hurt anyone so in my opinion and my former therapist opinion it is definitely okay. I even use the memory of her holding me when I have trouble sleeping — rare these days, and I've never had to take a substance to go to sleep.