I sympathise.
I got a HoD job in a secondary school some years back. Don't laugh...not until I had signed my contract was I told that my predecessor was being kept on, on a conserved salary.
Turned out he'd had an affair with an NQT and his wife had found out, whereupon he'd had a "breakdown". Let's just say that staffing was challenging until he eventually moved on.
Until then, he kept going off sick, meaning that I had to collapse classes, take turns teaching exam classes so that kids could get through their coursework, etc...
One Saturday, I was having a coffee in the city when I bumped into him and a blonde. He'd been off for a few days. "Oh, hello!" quoth I. "Glad you're feeling better. I'll see you on Monday." [I swear that I wasn't being sarcastic.]
"Nice to meet you, Mrs X," I added - at which point, she gave me a poisonous look.
Two years later, I met his actual wife...
All I can say, OP, is hang in there - it'll be hard work, but it'll get better.