First of all, I find this situation rather strange and unlikely, especially the amount of detail you put into your post.
If you're telling the truth then I definitely recommend seeing a therapist to help you sort out your feelings.
The only problem I can see here is if anything of what happened to you that day was against your consent, such as if you were forced or felt pressured to stay and participate/watch. In this case, discussing clear boundaries with your girlfriend would be extremely important as nobody should be forced to engage in or watch sexual activity of any kind without their consent.
Otherwise, it sounds like it's your mindset that is the problem here. Your girlfriend is not your property. What does it matter if the way she lost her virginity was sleazy in your opinion or not? I'd probably suggest that you find someone whose world view is more similar to yours but if you think of women as property then maybe staying single is best.