I'm wondering what is a make or break for a lot of relationships. Like for example, my best friend's girl has issues with the porn he likes...Annnnd considered breaking up with him over it. IMO its a strange reason to end a relationship.
What kinda porn is it? o.0
As for the question, people will tolerate a lot once they form a bond with someone, when someone else isn't tolerating some minor detail, it's usually indicative of a deeper underlying problem. For example, a specific type of porn.. (not saying this is the case for your friend, but just in general) The person doesn't really have a problem with the porn, they're irritated at something else, like maybe they work too much, or have poor hygiene, and the angry person just doesn't want to either admit it to themselves, or confront the other about it.
However, little annoying quirks may keep a bond from forming in the first place, so at the same time the small things can still be a make or break for relationships.