I wouldn’t tolerate mediocre sex tbh .
XP told me he used to be crap in bed with his ex as he was too selfish to prioritise her pleasure
I did day at the time, that’s on her for accepting that! She did cheat on him though, can’t blame her.
With me he’d spend up to an hour making sure I was fully satisfied, multiple orgasms every time, before he’d finish. Sometimes it was clearly an ego thing for him, he wanted to be “heroic” in bed as much as he wanted me to enjoy it.
Was with him for 9 years partly because I worried I’d never feel that way again. First guy I slept with after 6 months of singledom was amazing!! Barely knew him so no emotional connection at all, had sex the 2nd & 3rd time we met. Also multiple orgasms etc so I’m thinking maybe it’s just me 
XH before that was very good in the early days, although left me to finish it myself too often later on.
Other long term BFs and flings were all good, but only one stands out as amazing, a Spanish bus driver I shagged twice while working abroad. He was quite a bit older and knew his way around.
Plenty of ONSs that I was too drunk to notice or remember if they were any good tbh. But nobody who was actively crap or focussed solely on themselves would have made it past once.