The guy I like is with another girl. Should I stay away from him?

The guy I like is sweet, funny, really smart, and really attractive. Last year, he had a really difficult time and was drinking and smoking quite a bit, but I helped him turn it around and he is doing really well this year! In the process of all that, we became good friends and I began to really like him. We had quite a few “moments” and on New Year’s Eve he kissed me. Later, he didn’t bring it up, so I didn’t either, but I figured he had some sort of feelings for me. Unfortunately, this other girl in my school was really into him and asked him out. He said yes and they are now dating, although they aren’t officially together. I can’t help being jealous. Is it wrong of me to still spend time with him just as friends? I would never make a move when he’s together with someone else, but I really can’t help flirting a little. Should I just stay away from him right now? Should I give up on him?