“If Brad Pitt and Johnny Depp couldn’t make their marriages work out with bisexual women, why would some random dude imagine he can?”
I think you answered your own question back there when you pointed out that these are Hollywood relationships/marriages which are bound to end at some point for a wide number of reasons. Ending a relationship is not a sign of failure either, maybe those two people will follow their own paths to happiness either alone or with someone else.
And why are you assuming the guy is the only one that has to “make the relationship” work? Oh, let me make a wild guess: women are passive “agents” in relationships according your own vision, right?