Lost my virginity and I regret it

So I’m 18, and I’ve started talking to this guy about 3 months ago who is my best friends cousin. It was great, and we talked allll the time and hung out a lot. He would always ask to have sex and I would turn him down, but we would do other things. It was really special to me, and I wanted to lose it to someone that I was actually dating at least. Well yesterday, I went to his house for the first time and we ended up having sex. It wasn’t even that great and I regret it with all my heart. All I can do now is take this as a lesson to listen to my gut, I’m still upset that I wasted it on someone who wasn’t deserving of it. I don’t understand how I could be so stupid.

The worst part is that he’s taking to me less which makes me think he was just using me.

I guess I just wanted somewhere to vent, if you’ve gotten this far, thank you

also, sorry if I have posted this in the wrong group!