Historically, people with 3 letters in their name, such as Ian, have a severe case of BFPS. He does not get horny for skanks since they are skanky hoes.
BFP is usually short for "Big Fucking Psomething". But in referring to relationships, it's a play on words for BFF, "Best Friends Forever". BFP is "Best Friends for Pleasure". Similar to FWB "Friends with Benefits" but better friends and better benefits. FWB is usually a temporary situation, where BFP is more permanent. Like someone in an open relationship might have a BFP. They are your go-to people you trust for regularly having group sex.
That 3-way was the most amazing thing ever, so we're upgrading you from our Gym Buddy to a BFP relationship.
Baby-free pussy
Man, I am tired of messy around with women my age. I need some of that BFP. What is that? Some baby-free pussy.
"Damn... you see that chick with the bulge in her jeans over there? She's got one of those BFP's"
Big Fat Pussy. You've heard of a big fat cock...but have you heard of a big fat pussy.
"I subbed to this girl's OnlyFans and she has a BFP"
Bigger Fucking Problems, used as an explanation or excuse as to why something hasn't gotten done. Often used in context as if it were a pseudo-medical condition.
"No, I haven't mowed the lawn -- I've had a pretty severe case of BFP this month."
Big Fat Positive. Used in blogs where people are trying to conceive (TTC). It means you have a Big Fat Positive pregnancy test. Opposite of this would be BFN, which means Big Fat Negative. You have a negative pregnancy test.
I've been pretty convinced that I wouldn't see a bfp without the help of fertility specialist, but we conceived on our own.