I'll brave a battering on this one.
DP has been going through peri-menopause for a few years now. A good few health issues as a result, in particular a massive uptick in the frequency of her migraines. HRT seems to have helped massively over the last year or so.
For a good while, she was incredibly unpleasant to be around. Now I get why, she was having a shit time, she felt like crap almost constantly, she was miserable.
But even on the good days, she was still different. Her tone was sharper, she was quick to snap, things frustrated her more easily. Everyone else's problems were utterly unimportant, and hearing that I'd had a bad day in work just pissed her off even more. Even conversations where she was happy, when she was telling me about a lovely day out she'd had with DD, felt like they had this undercurrent of anger and frustration just from her tone.
After nearly a year of this she got upset one night because she felt like people were avoiding her. And she was right. DD was disappearing to her room instead of hanging out with us, her friends and family were often "busy" when she tried to organise something. My brother had asked me if he'd offended her because she kept being so short with him. I'd tried my best to ignore "the tone" as DD had come to call it, but some days I'd come home from work and know just from the "Hello" I got that tonight was a night to make myself scarce.
Obviously I can't "get it", I'm a man, I'm never going to have to deal with menopause, but I tried to empathise. Honestly though, I'm glad HRT helped DP so much, because I honestly don't know if I could have lived with that version of her for the next 5 - 10 years.
For contrast, about 6 years into our relationship DP was very ill, to the extent she was almost bedbound for the better part of a year. It was incredibly difficult, especially as DD was only 4. And obviously she was upset and miserable during that time. But I never considered leaving her then, never thought for a moment that I wouldn't spend the rest of my life with her. I can't say the same about what peri-menopause did to her.
DP's sister is a few years younger than her, and DP came home a few weeks ago from visiting her and told DD "Ok, I think I finally understand what you meant by 'the tone'"