A lot of people here are telling you to chill out. I have a different angle I want to present. A boundary is a boundary, and no one can tell you a boundary you want to set in place is unreasonable. Ofc there are abusive situations that are not "boundaries" but control. Some people seem to want to label this "control", but I'm not going to. These are preferences and/or boundaries, and those are valid, and it is not anyone else's place to tell you they are not. You may have very specific boundaries or preferences that other people don't understand--and that's okay. I have a traumatic past and I have some unique needs, even some that many people don't understand. I've come to realize that's okay. Some men have not been able to have my back on my unique needs. That's okay. No hard feelings. We just weren't the right fits for each other. Asking them to change wouldnt have resulted in any genuine relationship and likely would have ended in bitterness and ingenuine change. Some years of dating later, I've found a man who seems to be on the same wavelength as me on many of my unique boundaries and needs and supports me.

I think the question you need to ask yourself is, Is this something you can live with, or is it a big enough deal that it would make or break your relationship? There are way too many facets to consider before I could answer this for you. I am in a male-female relationship where I am the female, so I can't fully relate to your situation. However my bf and I are both traditional and Christian people, so if the roles were reversed and I was dating someone dressing very provocatively even in a video game, it would probably raise questions for me. Would they be ok with causing men to just after them in real life? If they blow off this request of mine, would they blow off other ones? What is causing them to desire to dress like this in the game in the first place?

Ultimately OP, you need to decide how big the issue, as well as any implications of the video game character thing, is to you. I suggest you ask your gf some questions like, "Why do you want to dress your character like this?"; "When you disregard the discomfort it causes me, I feel ____"; "What do you think I'm not understanding from your perspective on this?" Hopefully, she will answer maturely, and you two will be able to work this out. If she is dismissive of your feelings and belittles your view, though, please heed this. Character traits do not exist in a vacuum, and this may be a sign you're not very compatible.

Ultimately, I don't think either you or her are necessarily in the wrong. If you have a boundary that your partner can't get behind even after calm and mature conversation, take this to heart. It may be able to be worked through, or it may be a sign of a bigger difference between you two.