I almost stopped being friends with my best friend for a similar reason. He NEVER apologizes for his big screwups but often aplogizes for the littlest things that would not and had no chance at offending me. I can tell deep down he cares about me so I keep him around as a friend though and try not to think about how he's hurt me.The only friendships I've had with INTPs that have worked long term are ones which do not get too close. However, I've found most of them to get close/intense much more quickly than I would with anyone else (and as these have always been men, there's often a romantic tinge to the friendship). It's probably because we can actually talk about the things which interest us. These never end well, though; they don't necessarily end horribly, but they end & usually include some tiff.
One major problem is, these INTPs would never apologize & never admit when they were wrong. They'd always make some excuse instead of owning up to a mistake. This can be a weak spot in me also, but hanging out with them highlighted my compassionate & humble side. They'd also seem very unaware or in denial of their own emotional motivations. Emotional motivations come through loud & clear to an INFP, like nails on a chalkboard, and when someone claims they are objective or unbiased when they are not, it just seems delusional & arrogant. Basically, those tiffs which ended the relationship could have been resolved with a sincere apology & admitting of an irrational moment. I found myself making peace, but I never saw an effort on their part, so I'd cut them out of my life. It's needs to be a two-way street when it comes to compromise.