Every relationship has issues.
Heck, every individual has issues. Everyone has had some modicum of difficulty in life, or at the very least, felt unfairness, sadness, sorrow, shame, insecurities, and so on, and everyone has stuff that has been wrestled with and resolved. The fact that many people have found polyamory and pursued it as some kind of medicine to heal their relationship issues, and perhaps done more harm than good, doesn't mean that someone who is basically happy and fulfilled can't incorporate poly successfully into their life AND also have issues that need to be dealt with. Being human means being flexible and learning to have patience.
I have stated this before in other threads: I think that a lot of the time it is a tedious exercise to ask oneself, "am I poly or not?" I think it is more useful to stop worrying about labels and ask, "What kinds of relationships do I want in my life and how do I create them?"
You asked in the beginning of your post: what is in between identifying as poly and identifying as mono? I guess the way I see poly could be an in-between view. I prefer a more easygoing, relaxed approach, and just see it that people have the capacity to have a wide range of relationships while on this earth, and that it is the relationship that is either poly or not, not the person. A person's affinities and proclivities are influenced by many things in our lives and the cultures in which we live, as we grow to adulthood and beyond, and I don't see poly as something "hard-wired" into our brains. It's more a matter of how open and accepting you are of feelings you may have that perhaps will not fit into an unconventional relationship structure, and how willing you are to make poly a part of your life and take a chance in doing something that is not readily accepted in society.
I often point people to this FAQ from an old poly newsgroup:
From that FAQ, this is what I relate to the most:
"...the word "polyamorous" is, like all labels, just a tool. What you do and how you treat the people you love is probably more important to them, in the long run, than whether you fit a particular descriptive term, so don't sweat it, okay? And take good care of each other.
An alternate point of view:
There aren't polyamorous and monogamous people; there are polyamorous and monogamous relationships. The same person may at various times be happy in both monogamous and polyamorous relationships at various times in his/her life. What is right depends on you and your feelings, and the feelings of those you are involved in relationships with. You may at some times be involved in a relationship that is monogamous, and that may be the right thing for the people in that relationship; at other times, you may be in a relationship which works better as part of a polyamorous network of relationships. In any case, the important thing is probably to act kindly and responsibly, and to communicate clearly with intimate partners and potential partners about these issues. Don't deny your feelings or the feelings of those that you care about. Get in touch with how you and those you care about really feel, rather than how society wants you to feel, or how you think it would be logical to feel, or how you've been told polyamorous people (or monogamous people) should feel. Then behave in ways which are honest, and which make you, and the people you care about, and the people they care about, happy and fulfilled. If this results in you having more than one intimate relationship at the same time, or being involved in a relationship with more than two people, those who are big on categorizing and labeling people will label you a 'poly person'."