i think he means actual insertion. i'll call the 4 girls that live in the house, main girls. (Ophelia, Brenna, Catherine, Lucia)
he has yet to enter them. in the shed with Brenna, it was cut off before he entered. in the Scene with Ophelia, Catherine interrupts. he hasn't gotten close with Catherine and hasn't even done a scene with Lucia yet.
so i think he means, we will get a penetration scene with one of them? just a guess. it makes sense to give a sex scene with the side girls earlier. there's a saying going around there that if you give people what they want early, they will lose interest.