You're basically shooting yourself in the foot just by mentioning other guys, in a story where you've specifically made it so that the mc is the only male in the story. That's the whole reason for the controversy and why people are calling stuff like this NTR. If not NTR, it's bait and switch. If it was any other AVN, it wouldn't be as controversial, because they don't actively promote their game as having the mc be the only male in the story.
The girls don't have to be virgin, but you don't need to bring up past sexual relationships to know about the personality of the characters. It's just a turn off for people who like harems. No one wants to hear about being sloppy seconds, or whichever number mc is.
Also, I may be wrong in interpretation, but when Sasha is talking about her experience with the guy from the other school, isn't that basically the first time she's done it? You made it sound like she did. The way she was talking, was as if she did it for the first time, by saying the experience was something. And it feels like that was done around the same time she did the thing with MC. Not way in the past. But now in the comments you've said she has had multiple relationships with other men. So which is it?