Never. If I truly felt like the relationship wasn't working I would've had the balls to Atleast break it up with my girl and moved on. With that said this is a hentai. Logic and compassion is nearly non existent in this realm.
How would that work if he is not a virgin anymore? I highly doubt that after hearing the slut rant on about stealing guys first times he will just willing fall over heels for her.
Vise-versa. I would rather take the girl in the glasses over the other girl. The other girl looks like she'll lure you in with affection, take your shit, and bounce.