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I think this is what you are talking about http://www.mangago.me/read-manga/hana_to_akuma/. Not really sure about that.
You're looking for "Hana to Akuma"
beta
I think this is what you are talking about http://www.mangago.me/read-manga/hana_to_akuma/. Not really sure about that.
You're looking for "Hana to Akuma"
I do not know if it is this one or another, where the girl marries, has kids but she later dies leaving her teenage looking kids and her husband alone. I do not know if it is instead of vampire a demon but it might be.