I had to think about this long and hard.
INFJ's are very loyal.
However there are a couple trends that are apparent in relationship history of lots of the INFJ's on this site.
First and foremost seems to be the INFJ's tenacity when sticking to a relationship that is obviously failing. Lots of us have been in relationships that weren't good for us, and we've remained in those relatinoships for long periods of time because we feel some sort of obligation to make it work. Never say die, never give in......
Leads me to the conclusion that a INFJ seems to NOT give up a relationship, no matter how bad, as long as they are committed to the relationship.
Now, on the other hand, once an INFJ gives something up, those emotional strings are cut and we're just done with it. Flat done. We may try to remain friendly with our ex, but thats because we want to remain friendly with almost everyone. And once we've cut those strings, we're moving on.
If the INFJ eventually loses interest, they will terminate the relationship.