To give my two cents about the Nicki situation, first I honestly have to applaud NeonGhost's writing, that he was able to create all these characters and give them such varied personalities. As someone who has occasionally dabbled in writing fanfiction, let me tell you, that is not a small thing to do.
Second, for those who complain about Nicki, remember that she's essentially a young adult, can't remember what her age is but I think is around or over 22, with a string of failed relationships. Let's be honest now, at that age, how many of us can honestly say that we didn't make stupid decisions? Couple that with her not having much of a backbone, at that point, and Brent being an arrogant dudebro and you have a recipe for disaster.
And third, which I feel is the most important thing. This is a fictional story. In order to have an entertaining story, the characters need to have some flaws and behave in a stupid manner, otherwise there would be no plot. If Nicki were to behave responsibly from the start, tell Guy what's up and then dump Brett there and then, to live happily ever after, then people would complain that it's a boring story and Nicki is such a flat character.
I get that there is investing yourself in the story and caring about the characters. But at the end of the day, one has to remember that it is just a story and it's better to enjoy the ride, rather than bug the dev to cut out what is one of the most important characters to the story.
Because just as Geralt, Jamie Lannister and other characters went through their character developments, Nicki is doing the same thing in this story. I mean, once she came back into Guy's life, on the good path, she is trying to both find her place in life and show him that she can be relied on.