We had something serious now Im invisible what do I do? need serious help?

So this guy i dated for like 8 months broke up with me when he had to go back home for summer (we are in college) we had some problems but nothing huge no cheating, no disloyalty. I loved him so but he felt we just werent compatible .. now school is back in session and since it is a small school i see him everywhere and its always so awkward.. there was such a strong bond and now its like he doesnt even know me... he wont talk to me he will just give me a half *** smile and keep walking... it upsets me so much because it feels like i meant nothing... I didnt do anything foolish while he was gone. I know I need to move on and it takes time but I cant stand this feeling... I just want to talk to him, nothing about whats going on just chit chat. my friends say i need to wait like 3 weeks before i try talking to him again but its so hard. What is going on here? does this mean I meant nothing? I dont know what to say to him when it talk to him again... can anyone help me out please?