I don't know anything about Swedish law; I assume that they mean something like you being his 'common law wife'.
I suppose that this is the difference between living together as a married couple and actually being married. If you had been married, this would have made a difference to the outcome, but not to the feelings.
There are two things, at least, going on here.
1. Why he has gone ~ fault and blame etc.
2. Whether you should be treated like this, when you were his long-term partner.
Personally, I think that, if you do write to him, then you will need to keep the letter very low key ~ ie no hysterics.
I'm not recommending that you do or do not contact him ~ only you can make that decision. However, you should seek some non-judgemental advice, I think, for both of your sakes.
Maybe you could say
~That you understand why he has done this ~ because he finds your behaviour overly dramatic and difficult to cope with ~ but that he did say that he loved you, so you feel that he must surely be concerned about how things have been left with you.
~That your friends have suggested legal proceedings, as if you were his common law wife, but that the love you still have for him, in spite of your anger and sadness at what he has done, mean that you don't want to follow that path.
~That perhaps, when emotions are less raw, you can discuss the future again ~ even if, against your wishes but acknowledging his, this future has to be separate rather than together.
Yes, try to write a letter seeing things from his angle. You know that you can, because you have put it to us on this forum.
