I suggest that you give yourself some time to get over her, spend some time on yourself and give yourself some time to work out how you feel. It's natural and understandable for you to be feeling hurt and upset right now, give yourself some time, but if you are SURE you are ready for another relationship then go for it.
My advice is to try and avoid going out with people on the rebound, sometimes it does help you get over the person you have just lost, and you may find someone really special, but sometimes it can really hurt both of you.
I understand that you hate being single (I hate being single too, especially when everyone around me is in a relationship!) but try going out with your friends and enjoy being free and single. Don't go out looking for someone, but be open to the possibility that you might find someone, quite often people find someone really special when they aren't even looking!
Did she explain WHY she is feeling this way and just want you to be friends? Are you sure she actually has feelings for another guy? Or do you just think it is a possibility?
My thoughts are that if she really did love you, she would have explained exactly what had happened to make her feel this way.