This is just a rumor at the moment but it has been said that Utada is planning to marry a painter whose name is unknown at the moment. She has been seen with him many times in the past year and it is clear that they were dating. This could be why she wants to take such a long break from music.
The source is in Japanese and someone has only partially translated it, which is why I say it is possible and not absolute. I will edit this post accordingly once the full translation is available.
If it is true, I hope she lives happily with him
