This is something I cycle with - my husband had been diagnosed bipolar in 2010. There are elements that cross over into each thing, so it makes it hard to gauge. But, if you take an assessment of what they were like during the duration of your relationship and what you know of them before you were together, and compare whether or not there was a sudden change that is unlike any other time in their lives that you know of - you'll have about as good of an answer as you can get right now, with them still in this state of mind. I also check bipolar forums and websites for similarities and differences that may give me clues. There are NPD boards and sites as well that help.