What are we? Help!

I'm 20 years old, me and my co worker been working together for almost a year and we always flirt with each other but last week we finally got together it was not much just a casual hook up but it been driving me insane for the past week I don't know what we are. He's a real player and all my friends tell me to be careful but I just couldn't help it. He never told me he like me but we been talking for almost a year. Should I just ask him how he feel? But I don't want to sound clingy and I want to play it cool but it's just killing me inside. And I don't know if I should hook up with him anymore? I really like him so I don't want to seem too easy. What should I do?