Ladies, I do agree with much of what you say, but in my view, some points need revisiting.
Firstly, the “love it or leave it argument” works for either party or for none. Obviously, if two young people are in love with each other, neither wants to leave. So, as you say, there is a fine line between promoting modesty and controlling the wardrobe. However, this doesn’t mean that the young lady should basically be left alone and the young man should basically suck it up.
Secondly, to ascribe some controlling motivations to the opening poster is conjecture. It would be equivalent to saying that the young lady, his girlfriend, wants to look sexy, by a male poster. Conjecture is conjecture.
Now I need to deal with the argument that some men don’t want their women to look attractive to other men and for this reason limit their wardrobe. While I don’t deny that this may happen, we must realise first that modesty and lack of attractiveness are not the same thing and that one can look attractive while being modest. Modesty itself may be attractive (it is to me, for instance). While there might well be an urge of this kind in the Opening Poster’s attitude, the difference between the various kinds of looking attractive is important. For example, I would have no problem with a hypothetical girlfriend or wife of mine dressing up and wearing make-up and what is the purpose of this, if not looking more attractive than without it? However, I would have a problem if my hypothetical chosen lady saw it fit to wear somewhat revealing, sheer or particularly clingy clothes around men. A girlfriend is not a wife and she is single in the most basic sense, but a relationship entails a certain promise from which comes a right to expect that one won’t be seeking a specific kind of interest or appreciation from other men or other women. This is different from a concern for modesty, indeed, but it is not illegitimate. Since I used myself as an example for lack of other, you may of course respond freely without holding back.
At this point, it’s conjecture, but I take it that the Opening Poster decided to post because something is worrying him. If it were a trivial matter, he most likely wouldn’t care. If this is indeed a trivial matter but he still cares, well, his feelings need a bit of ease. And yes, I would suggest perhaps changing the focus a little and worrying maybe less about whether the girl (your girlfriend, Aball) commits this or that act of immodesty, especially in a slight degree, but rather focus on helping her grow spiritually. Therefore gently pointing her attention to the fact that some clothes could bring her the wrong kind of attention would be good, if done in charity and good faith (but be prepared to receive a similar kind of advice from her in humility), as would be bringing up the fact that he, the Opening Poster (i.e. you, Aball), feels a bit uncomfortable and perhaps insecure. It can be brought up in a loving way.
I would finally warn against letting it develop into a “who has a more modest girlfriend” kind of contest because modesty truly doesn’t rely on burkhas and the dress code is not the same as it was in 1th century Palestine.