Girls show interest and then blow me off, over and over again

Quick background. I'm a 21 year old male in college. The past three girls I've had a fling with have followed the exact same pattern of showing plenty of interest and inexplainably losing it at some point. I have spoken to some guy friends of mine and they are as baffled as I am. I will just go over the stories with these girls and perhaps we can figure out what I am doing wrong so I can improve myself (if I am doing anything wrong in the first place).

1. Ran into a high school classmate on campus, told me to call her up sometime. The next weekend I had a little party at my place so she came over with a friend and seemed to have a good time with my friends and I. The next week I asked her out for ice cream, but she was busy so I let it go. It was football season and our school is huge into the games so I invited her to come tailgating and stuff with some friends but she never did. I figured I'd give it a rest for a while, and the next weekend I was out of town and she randomly texted me asking what I was doing that night, and I obviously couldn't do anything. A week later I hit her up again to see if she wanted to hang, but she didn't want to for no apparent reason and the whole thing fizzled out.

2. Was set up with this girl who thought I was cute through my cousin. Never saw her in my daily life so I got to know her a little through fb and texting. Went out on a date with her to the movies and had a decent time, we both laughed and the conversation flowed pretty smoothly and she said she had a good time and wanted to get together after break. I hit her up like four days later just to see how things were going, but she never replied until a few days later. Replied to her message and same thing, no reply for a few days and it was rather brief. I called her to hang out with some friends that weekend, again no reply. Finally said **** it and quit talking to her. She did end up texting me a few weeks later, but I never tried making a move again as I was fed up with the bs earlier.

3. Met this girl that goes to my buddy's college about an hour away. He was home for the weekend so her and some friends had come. She thought I was hot and we had a decent conversation so I got her number. Chatted a bit over texting since she didn't live close. Ended up visiting her on the way through the town one weekend for a bit and things seemed to go alright. About two weeks later she told me I should come down there and hang one night and I decided to go since nothing was going on in my town. I went there and hung out with her, my buddy, and some of his friends from down there. She seemed interested and things went smoothly between us for the first few hours. Later in the night she started to kind of blow me off and didn't want to come out and really do anything, so I partied with my buddy and his friends. Slept with her although didn't really do anything since her roommate was in the same room. Next morning she had practice so I hung with my buddy for a while and she went to lunch after practice and never even made the effort to say goodbye or see me that day. Needless to say I was rather pissed off, but didn't blow up or anything. That was last weekend, I haven't made the effort to contact her since as that was a bs move imo.

Anyways, those are my stories. They thought I was good looking and initiated shit with me and talked and everything, but inexplicably started blowing me off at random times. I know I don't come off as a needy guy or a pushover. I usually try let them chase me for the most part and usually try to text them to set up dates and build some rapport, so I don't think I come off as desparate. I am fairly inexperienced with girls so I am a tad shy and hesitant to make a move on them, but I think I have a confident but reserved persona.

My buddies have all said that my game is fine and I act fine other than being a little bit shy and hesitant, which doesn't seem all that odd to me. Obviously, you aren't going to get every exact detail in this short novel, but is there perhaps something that I am doing wrong that none of us realize? Any suggestions for me that are related or not related to the topic? Thanks!