How to befriend guys in college without giving them the wrong impression

For context, I (F18) have grown up in a predominantly female environment (girl's school, etc) so I really don't know much about how guys function.

Throughout my life l've been told by both guys and girls that l'm attractive/pretty, and in public spaces men come up to me and ask me for my number/social media quite often. But l'm also not that outgoing or friendly, and have often heard that I seem pretty cold at first. However, since coming to uni, the vast majority of guys I became acquainted with have expressed some kind of attraction towards me or have asked me out, which is kind of becoming a problem because I keep losing friends due to it. For example, I had to distance myself from a guy I hung out with a couple times because he fell for me in the two weeks we've known each other. Another guy whom I considered a friend (I was actually really glad I became friends with him, as we are in the same dormitory) stopped talking to me because I turned him down when he asked me out. It's really a bummer because I make an effort to become friends with guys whom I think are nice people just for them to see me as a romantic interest which I do not reciprocate. It's not that easy for me to make friends in general, so it gets extra disappointing because I'm super happy whenever I feel like I've become friends with anyone. I don't consider myself flirty at all and if anything l'm a bit awkward due to a lack of guy friends in high school, as aforementioned. So I don't think (hope not?) I'm sending them some kind of signal that I'm into them as well. Is it true that guys and girls could never really be friends? Is there anything I should be cautious about when interacting with guys to make sure l'm not sending them the wrong signal?