So, 2020...
After I realised I was reacting to that shampoo, I also tried reducing my conditioner usage to very rarely. Then 2/3 of my hair fell out in a relatively short space of time (
alopecia areata, in conjunction with my eczema being the worst it'd been in 6 years, as if my immune system was hyperactive).
My relationship is basically on hold as my girlfriend couldn't keep up the long distance thing, so the stress of figuring that out may've contributed to the hair loss. Our connection is too strong for the story to be over though. There's a good chance it'll get back to how it was once I move back in a year or so or whenever the hell I can.
I saw a dermatologist and am now on an immunosuppressant (methotrexate). A bit early to tell how well it's working. I'd noticed some of the hair from my arms and other body parts had gone missing as well, but it's all started growing back now, apart from one large bald spot on my head which is only just starting to fill in, and one small one which hasn't at all yet. Might post photos once there's more difference.