User blog comment:B214/Question and Answers 2/@comment-4547267-20140328035516/@comment-24468758-20140330220400

The situations he was closest to graduate:

-with Rias in the sauna in Vol.10 (he screwed it up himself)

-with Akeno in Vol.7 before the final fight with Loki (he screwed it up himself, but it was for Akeno's sake that he intentionally screwed it up)

-after Rias' departure to Romania Akeno was ready to sleep with him despite Asia being next to them in Vol.14 (he screwed it up himself by revealing that that is not the kind of thin he and Rias where doing while sleeping together)

-in Vol.4 Xenovia tried to sleep with him (Rias, Akeno and Koneko dragged him away after interrupting them and threw him into the pool)

-even in Vol.2 with Rias as she asked him to take her virginity (they were interruped by Grayfia, who even badmouthed Issei before getting a better impression about him upon hearing that he is the Sekiryuutei shortly after).

Result:

He mostly screws it up himself and if he isn't the one to end the situation he screws it up by being overwhelmed and not seizing the opportunity.