In the minigame with Didac, before using your last condom (so before you for the second time) you had have to give Didac at least 4 orgasms. That way, before you put that last condom, Didac makes something to it...
Viewing post in Pact with a Witch (Hentai XXX, NSFW, +18) comments
Once she rips the condom, at the moment you cum, she is the one who removes the condom without you letting know what really happened.
In the ending is when all this is revealed, Didac confesses what he did, Neus is hearing it... and well... it's written for the patreon version, but not yet illustrated that part. The project right now is still onhold.