Zen Attitude by Sujata Massey

I just finished the second Rei Shimira mystery. It was a quick read - much more so than the first book. I'm still unsure about this series. It's better than some. I enjoy learning about Japanese culture. It's not a completely fluffy cozy mystery. Nonetheless, I can't say that I completely enjoy the books either.
I think my frustration has to do with the main character Rei. She's prickly. Her interactions with characters don't seem rational at times. Sometimes she's submissive to the point of annoying. And at other times she gets extremely angry and flies off the handle for less than rational reasons. Maybe this makes her more human... but I find it just makes her actions difficult to gauge.
In addition, much of the story revolves around her continuing relationship with Hugh Glendinning, the Scottish beau from the first novel, a character whom I really like. The two charcters' relationship is volatile. In the course of one book they are ridiculously happy, they break up, she moves out, he proposes, she considers saying yes. Realistically, most relationships don't function in that kind of order. In addition there is another character in the book - Angus, Hugh's brother - with whom Rei has an unstable relationship. Throughout the entire book she and he share a hate/hate relationship. Yet suddenly at the end she is laughing hysterically with him as though there was no tension all along.
So why do I keep reading? I'm pondering that myself. I will read the other Sujata Massey books sitting on my shelf. Even though I have other series that I have said I like better. I think it really revolves around the setting of the stories. I know very little about modern-day Japanese culture. Sujata Massey has a good way of describing a culture that I know little about. I would not sit down and read a non-fiction book about Japan, but I am curious to know more. In this story I did find out more about aspects of Japanese culture - in particular Zen temples.
What can I say. I don't have a good answer. I don't particularly like parts of these books. Maybe I just keep hoping they'll improve substantially over time.