ESA and long term flatmate issue

Hi there, I wonder if anyone can give me some advice? I am long term disabled and I have lived with my flatmate for just over a decade. We decided to share because my mental health team said that my social isolation was badly affecting my mental health and my OCD was exacerbating. During lockdown my flatmate was working from home and was being more helpful, and due to this ESA cut my disability premium. Today I called ESA as a nurse at my Pip assessment advised me that I should be on the disability premium. The advisor that spoke to me said she was sending me out a 'living together' form. I am now very anxious. We are not, and have never been a couple, he is out most of the time with his job and I am mostly housebound, but sharing a flat means we get a better living space than if we were to do it separately, and I am safer psychologically. Would we be classed as a couple just due to the fact we are the opposite sex? Our bedrooms are literally opposite sides of the flat, we don't share friends, but he helps me out if I'm in a bad way. He's my best friend, and tbh, I don't have many friends are I've been pretty isolated since I left psychiatric inpatient care. I'm terrified they're going to make me move or penalise me, or class us as a couple which obviously wouldn't be good for him as he lives his own life and I think it would be incredibly awkward for him, and also put a lot of pressure on him given he's just my flatmate. Does anyone know the law regarding this? It feels a little bit archaic to assume just because we are the opposite sex, we must be a couple...

Thank you for your help. It's embarrassing because he shouldn't even have to deal with these things and to be honest I don't want to end up living on my own because the department seem to assume no one can share a home without there being some sort of dodgy element. I only share as my psychiatrist felt it would be good to share with a friend who knew my issues rather than live alone as I was extremely isolated. We do do separate washing and cooking, so that's a relief, and obviously live opposite ends of the house. If we were a couple, I think we'd be a pretty poor example of a relationship, haha. I shall check out the sources you've shared.