Kind of a weird story. She doesn't want to bang him when she grows up again, but she also kind of does and she sets the entire mess off by approaching them and informing them that she's reincarnated. Also she's got an 'excuse' to be like that because she's extremely distant from her irresponsible single mother who hates her. But hey, if MC somehow manages to pull it off and get remarried then he'll be like 58 with an 18 year old wife, just like my japanese doujins. Then when he dies and reincarnates he can find her and then he can be the younger one, like an infinite relationship that never ends.
Honestly sometime I'd like to read a story about reincarnation (non-isekai because fuck isekai) where the main character fucking dies at the end and then gets reincarnated alongside the reincarnator. I guess spirit circle was ahead of its time like that but the ending sucked.