first time regrets

So recently I've been talking to a guy that seemed really interested in me. I really like him. When we hung out for the first time things went really fast. Up until this time I had said no to going any further than foreplay. I've never felt comfortable with a guy to the point of where I was willing to have sex. I had sex with him and have done so 3 times now. recently he has seemed less interested in me making me regret my decision to have sex with him. I don't know how to feel about our relationship (or lack there of) or my regrets about having sex.... any advice? Oh and I'm 19