I'm a sophomore at Virginia Tech and I'm also a university tour guide here, I get questions about this all the time. I have lived in a co-ed residence hall for almost two years now.
Here's the deal:
1. You will be in environments with both sexes in college, regardless of what building you live in. Even if it's a all guys dorm, girls will still be around.
2. You will be in environments with both sexes for the rest of your life. It's a part of growing up that you will have to get used to
3. Girls aren't stupid. Especially ones in college. I don't care how attractive you are, they aren't going to flock to you. Once again, that's life.
4. Living in a residence hall, especially with both sexes is great because it creates diversity. You will meet some incredible people in college. People from different walks of life, from different parts of the world, and all with unique views on this stage of their life. I have made some of my greatest friends, both guys and girls, living in the residence hall I do now. I have learned things from them I'd never imagine learning before. I would have never had this opportunity if I lived somewhere else.
5th and foremost: YOU HAVE TO MAKE YOUR OWN CHOICES. You are going to be put in environments that will test what you believe in all throughout college. Running from them doesn't fix anything. Trust yourself. If you don't want to have sex with a girl then don't do it. Period. College is a great time, but also a challenging one. A lot of growing up has to happen in a short amount of time.
P.S. Having sex in a residence hall is a great way to get in trouble with an RA, and most people will respect that