Full time work whilst caring for someone with Complex PTSD

Hi, I’m new here and hoping for some advice please. I currently support my best friend who lives with me who has Complex PTSD (officially diagnosed) which at times, makes him suicidal. I’m having issues at my full time employment (I’ve been here 8 years) for two reasons linked to this - firstly, they’re raising the issue of personal calls (in general but it was specifically pointed out to me about calls from him), and secondly, with my performance as my mental health is suffering (not because of my carers role). I am in the process of contacting my GP to register as an unpaid carer but looking into my rights with work, do they apply if I’m supporting someone with a mental health condition, not a physical one? My employer has no policy for carers and although my mental health is severe enough to be classed as a disability, they’re not being exactly supportive there so I suspect I’d only be allowed the bare minimum of support as an unpaid carer anyway.