So if you marry her, sure but the gf or actual friend, then no?
If we're in a committed relationship (GF, fiance, wife) then I'd be quick to tell her, assuming she's demonstrated that I can count on her in that fashion. I wouldn't particularly like it (pride/masculinity) but if anybody is supposed to be in my corner and hold me down during the bullshyt, it's wifey. It'd be difficult to get out of my own way initially, but why wouldn't I let her be there for me especially when I need her?
Ideally, it'd never get to the point where I'm fukking up the relationship because I can't get through something and just now decided to open up. At the very least, it'd be a, "Alright, look ... such and such is happening so if I'm not all the way here with you, that's why. I'm trying to get through it but it's rough."
Actual friend? They'd find out eventually.