Why did he lose interest?

A guy asked for my number in the club, texted the next day and we continued to communicate every now and then. I saw him a second time in the club and we talked a bit, but he never properly asked me out. Recently he saw me in the gym and he came over to say hi. We talked a bit but I got super nervous, I was nice but a bit aloof though. After that our communication has stopped. I tried to text him and even said sorry for being nervous that day. He responded to my text but did not put any more effort in it.. did not ask any questions and so on. Clearly he lost interest and now I am wondering if it was because I was so nervous or why? Was he only interested in something easy and realized I am not that kind of girl for a casual fling? He is really good looking, older than me and really confident.
Why did he lose interest?
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