Since we've been having so many threads about difficult relationships recently, I searched my personal library and relocated the books that have helped me most. I was involved in two extremely dysfunctional relationships in my younger days. Both partners turned out to be horrifically narcissistic although I was too naive and trusting at the time to recognize that the problems were THEIRS, not mine. I was traumatized and in a certain sense destroyed by remaining in these relationships even for the short time I did (4 and 5 months respectively).
Only recently have I begun to understand the dynamics of those involvements, thanks initially to a couple of books:
The Verbally Abusive Relationship - every case study sounded exactly like me, but I wouldn't have said I was being abused at the time.
When Your Perfect Partner Goes Perfectly Wrong - this one also had on-the-mark case studies, and it helped me to see why I'd been "suckered in" by these creeps.
I'm still angry about it, after nearly 20 years in one case, and I get mad when I read about others here who have some similar things going on. I'm not trying to diagnose anyone else's relationships, but if you or a friend are in a bad one, you might find help and understanding through such books.