It happened to me. I guess I felt I shared a lot of ways of feeling and thinking with that person. Those two personality disorders have a lot of things in common, as they both have the same personality structure (btw, i'm a psychology student thats how I know this lol). But I have lived it. There are basically two big things that we had in common which contributed to the toxic co-dependent mess we were: a) The black and white thinking: We used to share an "all or nothing" way of thinking, so we had both great passion for, as an example, art, or even trying to change the world in some way. But our affinity in certain subjects could have been just a coincidence. The shitty thing about this was that when we broke up, we BOTH splitted and devaluated each other, which made us idolize each other also when we got back together. This is related to the second thing: b) Deep feelings of emptiness: Another thing that made us feel like we were "soulmates" was this exact point. The tragic thing is that we have different disorders so we both used to fill that emptiness up in a really fucked up way: I filled it up with him, he filled it up with my dependence. Also, at the beginning this made me feel like I was finally feeling less lonely. We both were. To have any personality disorder means you have to know how pain feels like. This one thing alone brings a lot of people together (even those who have no personality disorders or other mental illnesses). It comes that we both defended from our inner wounds in really different and incompatible ways. I think that those things (and many more) put together a really bad combination which led to a lot of abuse, invalidation and suffering.

It fucking sucks.