People constantly think we're dating but...?

First I would like to point at that if you are aware of the fact that he has feelings for him, then you shouldn't flirt with. If you are flirting with him, you are giving him the impression that you are interested and just playing hard to get. Try to limit flirtations between you two and also try to spend less time with him. Have a serious talk with him that this will never work. Then you would give him space to get over you. You can still hang out with him, but keep it minimally low. Also tell him that when he is over you that y'all can start hanging out alot as friends. About the reaction you gave them you are sending the exact opposite message. When someone asks you if you are dating and you giggle and laugh, the person who asks is going to think that you guys really are in a relationship. They'll think that y'all are probably denying it to yourselves and you probably do have feelings for each other. Anyway next time if they ask the same question again make sure you have a serious face and say no.