@Nep I can see a couple scenarios. He falls in love with both and he has to choose which one stays. He falls in love with one personality and she is the one to fade away. He falls in love with both and they combine into a 3rd entity that has no recollection at all. Could be one personality love him while the other meets somebody else and she sticks with love interest B. She could also revert to her pre-DiD self and lose all memories from that point on. Or worst case scenario the stress from personality clashes leads to “murder” or otherwise death.
Hell for all we know we could have a full polygamy thing in the end.
Have you read Mahoraba? It also involved multiple personalities (in this case a total of five including main) with at least one or a few of one of your suggested endings. I generally consider that story a happy ending. Bittersweet endings are like Shishunki Bittersweet (ending 1)
Radiata Stories, various Kingdom Hearts games, various Star Ocean games, various Tales of games... probably need to add Gakkou Gurashi to this list soon -_-. It is where stuff are generally "not happy" such as someone meeting a tragic end/ not saved/ remain unhappy. It usually gives me a very VERY bad aftertaste. Since this involves multiple personalities my guesses are mostly like yours (fused personality, deaths, memory loss, etc) minus any "successful love stories" like being able to pick who goes away and then successfully getting the other personality.
Its really that or we meet new and more lovable characters that were created to suffer.
It sounds sad when one personality or rather a "person" just disappear. It is kinda similar to that one manga which mc can see girls that guys had crush with.
Just hope that it won't be triangle love or one-side love story from another personality or mc loves both of them, but I kinda expect one of the above to happen because of the title and to spice things up.
Please note: Due to a number of reasons, J.U.M is dropping this manga so we will not be translating any further chapters. Anyone interested please pick it up...