Thanks for the reply! I guess as long as the MC gets the choice of taking their virginities, it feels in character, as long as he's freely sharing, to have him not mind if they experiment other stuff (barring anal) first

The "check-in" scene makes a lot of sense and could have minimal impact if, for example, when you're asked if you're ok with the "next level" sharing, you're also asked about the "levels" you'd previously restricted. After all, while it makes sense to restrict kissing but allow other forms of physical contact, if that's your preference, it makes less sense to allow oral but not handjobs, so asking again about handjobs when you're asked about blowjobs, and so on, makes a lot of sense (but to each their own, if you make it possible, players could set temporary boundaries so they progress witth he girls first, but later give them permission).
I think you're going in a great direction and don't want to make suggestions that would derail that, so here's one that should probably have the lowest priority possible: while now the confidence build-up or removal makes sense as a way for the player to steer the story, how about implementing tradeoffs? Like a "confidence economy" where you can trade stuff that matters for confidence. For example, setting boundaries could cost 1 confidence - if the MC wants to be the greatest sharing chad there is, he's not bothered by petty boundaries, is he? I wonder if that would work. Could be offset by confidence-boosting events in the day but ultimately mean that on some days you may not have a net permanent confidence gain, or even have a net loss. Might make for a more dynamic gameplay? But would probably require a lot of testing to reach a good balance. Other aspects could be allowing the player to confess jealousy while interacting with the girls, which could lead to an cost+reward scenario, where you get a small bonus scene or a nice tease if you share a moment of insecurity with your girl. I don't mean a negative event but a positive one, she could feel aroused by making you jealous and even touched by your openness about it, so while it costs you -1 confidence, it gives you a hidden scene as a reward. Occasionaly, it could encourage the girl to give you a little extra ntrs tease, flirting with the idea of cheating your boundaries without going too far, with the single purpose to tease you and entirely controllable by your decisions. Or it could be a more romantic quick scene. A variety of both would be the most interesting. The idea is to make it not very consequential, but more of a chance to flavour your relationships roleplay wise, and to make use of an excess of confidence boosts to gain little interesting episodes - if this excess exists, as it seems, then you could keep a fully confident playthrough while "spending" a little extra confidence on these side episodes. Extra bonus scenes do cost time to write and produce, another good reason this would probably be a low priority, longer time frame idea to consider.
Best of luck!