I haven't been told it but definitely self-identify! It looks like being very insecure (convinced I'm not worth the person's time or attention and they'll probably leave me, probably for someone better, eventually). I can be clingy, jealous and need a lot of reassurance. There's a lot of inner turmoil, massive rumination, almost obsessing about the person. I hate conflict as I feel every argument means the end of the relationship. I hate the feeling of attaching to someone and it playing out in this way. It's particularly intense in new relationships, as the attachment process is happening.
For me it only really plays out with men (I'm in a committed relationship by the way and we've now found a good balance and I am not affected with my partner - I have developed a "secure" attachment with him, but the first three-four years were hard!). The root is that I had a very emotionally unavailable father who bullied and belittled me and made it very clear I wasn't worth his time (or much of his anything really...) and so I am constantly trying to obtain the secure love of a man. It is an awful situation!
I'm currently seeing a therapist who uses attachment therapy, the idea being that my Inner Child develops a secure attachment to my lovely therapist who offers me all the things my father could not, and eventually, very slowly, heal the wound so that hopefully (please god!) it stops playing out in my everday life. Dare I say it, it's slowly but surely working. I was super hesitant to see a male therapist using such a deep therapy technique, as it is very raw and intense and deep and difficult at times, but I feel we're coming out of that and have developed a really wonderful, healing, intimate and healthy relationship. It's amazing to know that someone will be there for me no matter what, and expresses his feelings for me in an honest but safe way, and who I can express my feelings towards without being labelled "intense", "needy", "demanding" etc. I wish I had started seeing him 10 years ago.
I haven't read any books myself, there's so much information on the internet, but there's a book called "Attached" which lots of people have found useful. But self-awareness is the most crucial step!
Good luck :)