I think they can be related. I'm not sure what it stems from - intensity of emotion? Unhealthy attachment style?
In my case, normally I'm relaxed about a lot of things, even things which bother many other people, and I let them go and wouldn't really get offended over them (though sometimes I do take things too personally, but I can usually write those off if I make an effort to be logical about it.) However, if there's been a big buildup of inconsiderate behaviour or if someone has seriously hurt me emotionally, I do have a bad tendency to hold onto grudges. Sometimes for years. It's not good, it's something I need to work on, it's damaging to me, but it's there. There are situations in which I'm unlikely to ever fully forgive a person.
As well, I am a very loyal friend/relationship partner, which I think is a good quality. But I have also found that partly for that reason I have trouble leaving unhealthy relationships and friendships. I get over-attached, in a way. I feel like I should just hang in there and work at it some more (even if the other person plainly doesn't care about working at it), I don't want to be abandoned, I love/care about them too much (or my idea of them) to give it up - that sort of thing.
I do wonder if it's some kind of unhealthy attachment thing...