User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-66.176.83.18-20150129224753/@comment-73.178.133.185-20150131201730

@anon2  Correction, they will get married after Issei becomes a High-class Devil. That is to say, he won't be able to marry her until then (as stated elsewhere, Dekram Bael won't even let Issei proclaim his love for her until he reaches this point). It won't necessarily be that they marry as soon as he is made a High-class Devil, which intentional or not is what your reply can be interpreted to mean.