Well if it was MPD(dissociative identity disorder) and he completely switches to another personality and doesn't remember,it would have been happening throughout the entire time you have known him.It's not something that would suddenly come about one day out of the blue,DID develops in childhood and not in adulthood.

IDK,to be honest,when I read all of this I started thinking it all sounds like bs.It sounds like he's using his illness as an excuse.That he's wanting you in his life when it's convenient for him,and when he doesn't,the other 'personality' is the excuse.

I was also thinking that since you hardly see him or anything,it's possible you're just getting played.A "soulmate" would be in your life all the time,would do whatever is necessary to be with you,be by your side.And a "soul mate" has to go both ways,2 souls meant to be together,so you may feel he's your soul mate but obviously he does not feel the same,so therefore it's not really soulmates.

It also seems too convenient that he knows ahead of time when he's not going to be himself yet claims amnesia when the other "personality" takes over.

Do you even have proof that he's been hospitalized,been diagnosed with anything at all?From the way it sounds you have never even lived with him and are in different countries.He could be/say anything he wants and how would you even know the difference or even know what's true?

You say you don't want to leave him but it sounds like you've never even really been together to begin with.