I’ve only had a few partners and thankfully never had this problem. I did hook up once with a girl with vaginismus, but we didn’t even attempt PIV sex because even fingering was painful for her. Poor girl! Anyway, that was more of a case of her being too tight rather than my cock too big.
As far as oral goes, I’ve only had one girl who was able to fully deepthroat me and touch my navel with the tip of her nose. Honestly, I still think about that night all the time when I’m jerking off—there’s just something so amazing about having your cock totally buried in someone’s throat. Gotta give my wife credit, though; she's been extra determined to take all of me lately, and has about ~1.5” to go.